This document covers the configuration language as implemented in the version
specified above. It does not provide any hints, examples, or advice. For such
documentation, please refer to the Reference Manual or the Architecture Manual.
The summary below is meant to help you find sections by name and navigate
through the document.

Note to documentation contributors :
    This document is formatted with 80 columns per line, with even number of
    spaces for indentation and without tabs. Please follow these rules strictly
    so that it remains easily printable everywhere. If a line needs to be
    printed verbatim and does not fit, please end each line with a backslash
    ('\') and continue on next line, indented by two characters. It is also
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    closing angle brackets ('>>>') in order to emphasize the difference between
    inputs and outputs when they may be ambiguous. If you add sections,
    please update the summary below for easier searching.

When HAProxy is running in HTTP mode, both the request and the response are
fully analyzed and indexed, thus it becomes possible to build matching criteria
on almost anything found in the contents.

However, it is important to understand how HTTP requests and responses are
formed, and how HAProxy decomposes them. It will then become easier to write
correct rules and to debug existing configurations.

First, HTTP is standardized by a series of RFC that HAProxy follows as closely
as possible:
  - RFC 9110: HTTP Semantics (explains the meaning of protocol elements)
  - RFC 9111: HTTP Caching (explains the rules to follow for an HTTP cache)
  - RFC 9112: HTTP/1.1 (representation, interoperability rules, security)
  - RFC 9113: HTTP/2   (representation, interoperability rules, security)
  - RFC 9114: HTTP/3   (representation, interoperability rules, security)

In addition to these, RFC 8999 to 9002 specify the QUIC transport layer used by
the HTTP/3 protocol.

The HTTP protocol is transaction-driven. This means that each request will lead
to one and only one response. Originally, with version 1.0 of the protocol,
there was a single request per connection: a TCP connection is established from
the client to the server, a request is sent by the client over the connection,
the server responds, and the connection is closed. A new request then involves
a new connection :

  [CON1] [REQ1] ... [RESP1] [CLO1] [CON2] [REQ2] ... [RESP2] [CLO2] ...

In this mode, often called the "HTTP close" mode, there are as many connection
establishments as there are HTTP transactions. Since the connection is closed
by the server after the response, the client does not need to know the content
length, it considers that the response is complete when the connection closes.
This also means that if some responses are truncated due to network errors, the
client could mistakenly think a response was complete, and this used to cause
truncated images to be rendered on screen sometimes.

Due to the transactional nature of the protocol, it was possible to improve it
to avoid closing a connection between two subsequent transactions. In this mode
however, it is mandatory that the server indicates the content length for each
response so that the client does not wait indefinitely. For this, a special
header is used: "Content-length". This mode is called the "keep-alive" mode,
and arrived with HTTP/1.1 (some HTTP/1.0 agents support it), and connections
that are reused between requests are called "persistent connections":

  [CON] [REQ1] ... [RESP1] [REQ2] ... [RESP2] [CLO] ...

Its advantages are a reduced latency between transactions, less processing
power required on the server side, and the ability to detect a truncated
response. It is generally faster than the close mode, but not always because
some clients often limit their concurrent connections to a smaller value, and
this compensates less for poor network connectivity. Also, some servers have to
keep the connection alive for a long time waiting for a possible new request
and may experience a high memory usage due to the high number of connections,
and closing too fast may break some requests that arrived at the moment the
connection was closed.

In this mode, the response size needs to be known upfront so that's not always
possible with dynamically generated or compressed contents. For this reason
another mode was implemented, the "chunked mode", where instead of announcing
the size of the whole size at once, the sender only advertises the size of the
next "chunk" of response it already has in a buffer, and can terminate at any
moment with a zero-sized chunk. In this mode, the Content-Length header is not
used.

Another improvement in the communications is the pipelining mode. It still uses
keep-alive, but the client does not wait for the first response to send the
second request. This is useful for fetching large number of images composing a
page :

  [CON] [REQ1] [REQ2] ... [RESP1] [RESP2] [CLO] ...

This can obviously have a tremendous benefit on performance because the network
latency is eliminated between subsequent requests. Many HTTP agents do not
correctly support pipelining since there is no way to associate a response with
the corresponding request in HTTP. For this reason, it is mandatory for the
server to reply in the exact same order as the requests were received. In
practice, after several attempts by various clients to deploy it, it has been
totally abandoned for its lack of reliability on certain servers. But it is
mandatory for servers to support it.

The next improvement is the multiplexed mode, as implemented in HTTP/2 and
HTTP/3. In this mode, multiple transactions (i.e. request-response pairs) are
transmitted in parallel over a single connection, and they all progress at
their own speed, independent from each other. With multiplexed protocols, a new
notion of "stream" was introduced, to represent these parallel communications
happening over the same connection. Each stream is generally assigned a unique
identifier for a given connection, that is used by both endpoints to know where
to deliver the data. It is fairly common for clients to start many (up to 100,
sometimes more) streams in parallel over a same connection, and let the server
sort them out and respond in any order depending on what response is available.
The main benefit of the multiplexed mode is that it significantly reduces the
number of round trips, and speeds up page loading time over high latency
networks. It is sometimes visible on sites using many images, where all images
appear to load in parallel.

These protocols have also improved their efficiency by adopting some mechanisms
to compress header fields in order to reduce the number of bytes on the wire,
so that without the appropriate tools, they are not realistically manipulable
by hand nor readable to the naked eye like HTTP/1 was. For this reason, various
examples of HTTP messages continue to be represented in literature (including
this document) using the HTTP/1 syntax even for newer versions of the protocol.

HTTP/2 suffers from some design limitations, such as packet losses affecting
all streams at once, and if a client takes too much time to retrieve an object
(e.g. needs to store it on disk), it may slow down its retrieval and make it
impossible during this time to access the data that is pending behind it. This
is called "head of line blocking" or "HoL blocking" or sometimes just "HoL".

HTTP/3 is implemented over QUIC, itself implemented over UDP. QUIC solves the
head of line blocking at the transport level by means of independently handled
streams. Indeed, when experiencing loss, an impacted stream does not affect the
other streams, and all of them can be accessed in parallel. QUIC also provides
connection migration support but currently haproxy does not support it.

By default HAProxy operates in keep-alive mode with regards to persistent
connections: for each connection it processes each request and response, and
leaves the connection idle on both sides between the end of a response and the
start of a new request. When it receives HTTP/2 connections from a client, it
processes all the requests in parallel and leaves the connection idling,
waiting for new requests, just as if it was a keep-alive HTTP connection.

HAProxy essentially supports 3 connection modes :
  - keep alive    : all requests and responses are processed, and the client
                    facing and server facing connections are kept alive for new
                    requests. This is the default and suits the modern web and
                    modern protocols (HTTP/2 and HTTP/3).

  - server close  : the server-facing connection is closed after the response.

  - close         : the connection is actively closed after end of response on
                    both sides.

In addition to this, by default, the server-facing connection is reusable by
any request from any client, as mandated by the HTTP protocol specification, so
any information pertaining to a specific client has to be passed along with
each request if needed (e.g. client's source address etc). When HTTP/2 is used
with a server, by default HAProxy will dedicate this connection to the same
client to avoid the risk of head of line blocking between clients.

Inside HAProxy, the terminology has evolved a bit over the ages to follow the
evolutions of the HTTP protocol and its usages. While originally there was no
significant difference between a connection, a session, a stream or a
transaction, these ones clarified over time to match closely what exists in the
modern versions of the HTTP protocol, though some terms remain visible in the
configuration or the command line interface for the purpose of historical
compatibility.

Here are some definitions that apply to the current version of HAProxy:

  - connection: a connection is a single, bidiractional communication channel
    between a remote agent (client or server) and haproxy, at the lowest level
    possible. Usually it corresponds to a TCP socket established between a pair
    of IP and ports. On the client-facing side, connections are the very first
    entities that are instantiated when a client connects to haproxy, and rules
    applying at the connection level are the earliest ones that apply.

  - session: a session adds some context information associated with a
    connection. This includes and information specific to the transport layer
    (e.g. TLS keys etc), or variables. This term has long been used inside
    HAProxy to denote end-to-end HTTP/1.0 communications between two ends, and
    as such it remains visible in the name of certain CLI commands or
    statistics, despite representing streams nowadays, but the help messages
    and descriptions try to make this unambiguous. It is still valid when it
    comes to network-level terminology (e.g. TCP sessions inside the operating
    systems, or TCP sessions across a firewall), or for non-HTTP user-level
    applications (e.g. a telnet session or an SSH session). It must not be
    confused with "application sessions" that are used to store a full user
    context in a cookie and require to be sent to the same server.

  - stream: a stream exactly corresponds to an end-to-end bidirectional
    communication at the application level, where analysis and transformations
    may be applied. In HTTP, it contains a single request and its associated
    response, and is instantiated by the arrival of the request and is finished
    with the end of delivery of the response. In this context there is a 1:1
    relation between such a stream and the stream of a multiplexed protocol. In
    TCP communications there is a single stream per connection.

  - transaction: a transaction is only a pair of a request and the associated
    response. The term was used in conjunction with sessions before the streams
    but nowadays there is a 1:1 relation between a transaction and a stream. It
    is essentially visible in the variables' scope "txn" which is valid during
    the whole transaction, hence the stream.

  - request: it designates the traffic flowing from the client to the server.
    It is mainly used for HTTP to indicate where operations are performed. This
    term also exists for TCP operations to indicate where data are processed.
    Requests often appear in counters as a unit of traffic or activity. They do
    not always imply a response (e.g. due to errors), but since there is no
    spontaneous responses without requests, requests remain a relevant metric
    of the overall activity. In TCP there are as many requests as connections.

  - response: this designates the traffic flowing from the server to the
    client, or sometimes from HAProxy to the client, when HAProxy produces the
    response itself (e.g. an HTTP redirect).

  - service: this generally indicates some internal processing in HAProxy that
    does not require a server, such as the stats page, the cache, or some Lua
    code to implement a small application. A service usually reads a request,
    performs some operations and produces a response.

First, let's consider this HTTP request :

  Line     Contents
  number
     1     GET /serv/login.php?lang=en&profile=2 HTTP/1.1
     2     Host: www.mydomain.com
     3     User-agent: my small browser
     4     Accept: image/jpeg, image/gif
     5     Accept: image/png

Line 1 is the "request line". It is always composed of 3 fields :

  - a METHOD      : GET
  - a URI         : /serv/login.php?lang=en&profile=2
  - a version tag : HTTP/1.1

All of them are delimited by what the standard calls LWS (linear white spaces),
which are commonly spaces, but can also be tabs or line feeds/carriage returns
followed by spaces/tabs. The method itself cannot contain any colon (':') and
is limited to alphabetic letters. All those various combinations make it
desirable that HAProxy performs the splitting itself rather than leaving it to
the user to write a complex or inaccurate regular expression.

The URI itself can have several forms :

  - A "relative URI" :

      /serv/login.php?lang=en&profile=2

    It is a complete URL without the host part. This is generally what is
    received by servers, reverse proxies and transparent proxies.

  - An "absolute URI", also called a "URL" :

      http://192.168.0.12:8080/serv/login.php?lang=en&profile=2

    It is composed of a "scheme" (the protocol name followed by '://'), a host
    name or address, optionally a colon (':') followed by a port number, then
    a relative URI beginning at the first slash ('/') after the address part.
    This is generally what proxies receive, but a server supporting HTTP/1.1
    must accept this form too.

  - a star ('*') : this form is only accepted in association with the OPTIONS
    method and is not relayable. It is used to inquiry a next hop's
    capabilities.

  - an address:port combination : 192.168.0.12:80
    This is used with the CONNECT method, which is used to establish TCP
    tunnels through HTTP proxies, generally for HTTPS, but sometimes for
    other protocols too.

In a relative URI, two sub-parts are identified. The part before the question
mark is called the "path". It is typically the relative path to static objects
on the server. The part after the question mark is called the "query string".
It is mostly used with GET requests sent to dynamic scripts and is very
specific to the language, framework or application in use.

HTTP/2 and HTTP/3 do not convey a version information with the request, so the
version is assumed to be the same as the one of the underlying protocol (i.e.
"HTTP/2"). In addition, these protocols do not send a request line as one part,
but split it into individual fields called "pseudo-headers", whose name start
with a colon, and which are conveniently reassembled by HAProxy into an
equivalent request line. For this reason, request lines found in logs may
slightly differ between HTTP/1.x and HTTP/2 or HTTP/3.

The headers start at the second line. They are composed of a name at the
beginning of the line, immediately followed by a colon (':'). Traditionally,
an LWS is added after the colon but that's not required. Then come the values.
Multiple identical headers may be folded into one single line, delimiting the
values with commas, provided that their order is respected. This is commonly
encountered in the "Cookie:" field. A header may span over multiple lines if
the subsequent lines begin with an LWS. In the example in 1.3, lines 4 and 5
define a total of 3 values for the "Accept:" header. Finally, all LWS at the
beginning or at the end of a header are ignored and are not part of the value,
as per the specification.

Contrary to a common misconception, header names are not case-sensitive, and
their values are not either if they refer to other header names (such as the
"Connection:" header). In HTTP/2 and HTTP/3, header names are always sent in
lower case, as can be seen when running in debug mode. Internally, all header
names are normalized to lower case so that HTTP/1.x and HTTP/2 or HTTP/3 use
the exact same representation, and they are sent as-is on the other side. This
explains why an HTTP/1.x request typed with camel case is delivered in lower
case.

The end of the headers is indicated by the first empty line. People often say
that it's a double line feed, which is not exact, even if a double line feed
is one valid form of empty line.

Fortunately, HAProxy takes care of all these complex combinations when indexing
headers, checking values and counting them, so there is no reason to worry
about the way they could be written, but it is important not to accuse an
application of being buggy if it does unusual, valid things.

Important note:
   As suggested by RFC7231, HAProxy normalizes headers by replacing line breaks
   in the middle of headers by LWS in order to join multi-line headers. This
   is necessary for proper analysis and helps less capable HTTP parsers to work
   correctly and not to be fooled by such complex constructs.

An HTTP response looks very much like an HTTP request. Both are called HTTP
messages. Let's consider this HTTP response :

  Line     Contents
  number
     1     HTTP/1.1 200 OK
     2     Content-length: 350
     3     Content-Type: text/html

As a special case, HTTP supports so called "Informational responses" as status
codes 1xx. These messages are special in that they don't convey any part of the
response, they're just used as sort of a signaling message to ask a client to
continue to post its request for instance. In the case of a status 100 response
the requested information will be carried by the next non-100 response message
following the informational one. This implies that multiple responses may be
sent to a single request, and that this only works when keep-alive is enabled
(1xx messages appeared in HTTP/1.1). HAProxy handles these messages and is able
to correctly forward and skip them, and only process the next non-100 response.
As such, these messages are neither logged nor transformed, unless explicitly
state otherwise. Status 101 messages indicate that the protocol is changing
over the same connection and that HAProxy must switch to tunnel mode, just as
if a CONNECT had occurred. Then the Upgrade header would contain additional
information about the type of protocol the connection is switching to.

Line 1 is the "response line". It is always composed of 3 fields :

  - a version tag : HTTP/1.1
  - a status code : 200
  - a reason      : OK

The status code is always 3-digit. The first digit indicates a general status :
 - 1xx = informational message to be skipped (e.g. 100, 101)
 - 2xx = OK, content is following   (e.g. 200, 206)
 - 3xx = OK, no content following   (e.g. 302, 304)
 - 4xx = error caused by the client (e.g. 401, 403, 404)
 - 5xx = error caused by the server (e.g. 500, 502, 503)

Status codes greater than 599 must not be emitted in communications, though
certain agents may produce them in logs to report their internal statuses.
Please refer to RFC9110 for the detailed meaning of all such codes. HTTP/2 and
above do not have a version tag and use the ":status" pseudo-header to report
the status code.

The "reason" field is just a hint, but is not parsed by clients. Anything can
be found there, but it's a common practice to respect the well-established
messages. It can be composed of one or multiple words, such as "OK", "Found",
or "Authentication Required". It does not exist in HTTP/2 and above and is
not emitted there. When a response from HTTP/2 or above is transmitted to an
HTTP/1 client, HAProxy will produce such a common reason field that matches
the status code.

HAProxy may emit the following status codes by itself :

  Code  When / reason
   200  access to stats page, and when replying to monitoring requests
   301  when performing a redirection, depending on the configured code
   302  when performing a redirection, depending on the configured code
   303  when performing a redirection, depending on the configured code
   307  when performing a redirection, depending on the configured code
   308  when performing a redirection, depending on the configured code
   400  for an invalid or too large request
   401  when an authentication is required to perform the action (when
        accessing the stats page)
   403  when a request is forbidden by a "http-request deny" rule
   404  when the requested resource could not be found
   408  when the request timeout strikes before the request is complete
   410  when the requested resource is no longer available and will not
        be available again
   413  when a HTTP/1.0 GET/HEAD/DELETE requests has a payload, also see
        the "h1-accept-payload-with-any-method" option
   500  when HAProxy encounters an unrecoverable internal error, such as a
        memory allocation failure, which should never happen
   501 when HAProxy is unable to satisfy a client request because of an
       unsupported feature
   502  when the server returns an empty, invalid or incomplete response, or
        when an "http-response deny" rule blocks the response.
   503  when no server was available to handle the request, or in response to
        monitoring requests which match the "monitor fail" condition
   504  when the response timeout strikes before the server responds

The error 4xx and 5xx codes above may be customized (see "errorloc" in section
4.2). Other status codes can be emitted on purpose by specific actions (see the
"deny", "return" and "redirect
This keyword is available in sections :
Alphabetically sorted keywords reference
Alphabetically sorted actions reference" actions in section 4.3 for example).

Response headers work exactly like request headers, and as such, HAProxy uses
the same parsing function for both. Please refer to paragraph 1.3.2 for more
details.

HAProxy's configuration process involves 3 major sources of parameters :

  - the arguments from the command-line, which always take precedence
  - the configuration file(s), whose format is described here
  - the running process's environment, in case some environment variables are
    explicitly referenced

The configuration file follows a fairly simple hierarchical format which obey
a few basic rules:

  1. a configuration file is an ordered sequence of statements

  2. a statement is a single non-empty line before any unprotected "#" (hash)

  3. a line is a series of tokens or "words" delimited by unprotected spaces or
     tab characters

  4. the first word or sequence of words of a line is one of the keywords or
     keyword sequences listed in this document

  5. all other words are all arguments of the first one, some being well-known
     keywords listed in this document, others being values, references to other
     parts of the configuration, or expressions

  6. certain keywords delimit a section inside which only a subset of keywords
     are supported

  7. a section ends at the end of a file or on a special keyword starting a new
     section

This is all that is needed to know to write a simple but reliable configuration
generator, but this is not enough to reliably parse any configuration nor to
figure how to deal with certain corner cases.

First, there are a few consequences of the rules above. Rule 6 and 7 imply that
the keywords used to define a new section are valid everywhere and cannot have
a different meaning in a specific section. These keywords are always a single
word (as opposed to a sequence of words), and traditionally the section that
follows them is designated using the same name. For example when speaking about
the "global section", it designates the section of configuration that follows
the "global" keyword. This usage is used a lot in error messages to help locate
the parts that need to be addressed.

A number of sections create an internal object or configuration space, which
requires to be distinguished from other ones. In this case they will take an
extra word which will set the name of this particular section. For some of them
the section name is mandatory. For example "frontend foo" will create a new
section of type "frontend" named "foo". Usually a name is specific to its
section and two sections of different types may use the same name, but this is
not recommended as it tends to complexify configuration management.

A direct consequence of rule 7 is that when multiple files are read at once,
each of them must start with a new section, and the end of each file will end
a section. A file cannot contain sub-sections nor end an existing section and
start a new one.

Rule 1 mentioned that ordering matters. Indeed, some keywords create directives
that can be repeated multiple times to create ordered sequences of rules to be
applied in a certain order. For example "tcp-request" can be used to alternate
"accept" and "reject" rules on varying criteria. As such, a configuration file
processor must always preserve a section's ordering when editing a file. The
ordering of sections usually does not matter except for the global section
which must be placed before other sections, but it may be repeated if needed.
In addition, some automatic identifiers may automatically be assigned to some
of the created objects (e.g. proxies), and by reordering sections, their
identifiers will change. These ones appear in the statistics for example. As
such, the configuration below will assign "foo" an ID number smaller than its
"bar" counterpart. This will be swapped if the two sections are reversed:

     listen foo
         bind :80

     listen bar
         bind :81

Another important point is that according to rules 2 and 3 above, empty lines,
spaces, tabs, and comments following and unprotected "#" character are not part
of the configuration as they are just used as delimiters. This implies that the
following configurations are strictly equivalent:

         global#this is the global section
     daemon#daemonize
         frontend         foo
     mode             http   # or tcp

and:

     global
         daemon

     # this is the public web frontend
     frontend foo
         mode http

The common practice is to align to the left only the keyword that initiates a
new section, and indent (i.e. prepend a tab character or a few spaces) all
other keywords so that it's instantly visible that they belong to the same
section (as done in the second example above). Placing comments before a new
section helps the reader decide if it's the desired one. Leaving a blank line
at the end of a section also visually helps spotting the end when editing it.

Tabs are very convenient for indent but they do not copy-paste well. If spaces
are used instead, it is recommended to avoid placing too many (2 to 4) so that
editing in field doesn't become a burden with limited editors that do not
support automatic indent.

In the early days it used to be common to see arguments split at fixed tab
positions because most keywords would not take more than two arguments. With
modern versions featuring complex expressions this practice does not stand
anymore, and is not recommended.

In modern configurations, some arguments require the use of some characters
that were previously considered as pure delimiters. In order to make this
possible, HAProxy supports character escaping by prepending a backslash ('\')
in front of the character to be escaped, weak quoting with double quotes ("")
around a piece of text, and strong quoting with single quotes ('') around a
piece of text.

This is pretty similar to what is done in a number of programming languages and
very close to what is commonly encountered in Bourne shell. The principle is
the following: while the configuration parser cuts the lines into words, it
also takes care of quotes and backslashes to decide whether a character is a
delimiter or is the raw representation of this character within the current
word. The escape character is then removed, the quotes are removed, and the
remaining word is used as-is as a keyword or argument for example.

If a backslash is needed in a word, it must either be escaped using itself
(i.e. double backslash) or be strongly quoted.

Escaping outside quotes is achieved by preceding a special character by a
backslash ('\'):

  \    to mark a space and differentiate it from a delimiter
  \#   to mark a hash and differentiate it from a comment
  \\   to use a backslash
  \'   to use a single quote and differentiate it from strong quoting
  \"   to use a double quote and differentiate it from weak quoting

In addition, a few non-printable characters may be emitted using their usual
C-language representation:

  \n   to insert a line feed (LF, character \x0a or ASCII 10 decimal)
  \r   to insert a carriage return (CR, character \x0d or ASCII 13 decimal)
  \t   to insert a tab (character \x09 or ASCII 9 decimal)
  \xNN to insert character having ASCII code hex NN (e.g \x0a for LF).

Weak quoting is achieved by surrounding double quotes ("") around the character
or sequence of characters to protect. Weak quoting prevents the interpretation
of:

       space or tab as a word separator
  '    single quote as a strong quoting delimiter
  #    hash as a comment start

Weak quoting permits the interpretation of environment variables (which are not
evaluated outside of quotes) by preceding them with a dollar sign ('$'). If a
dollar character is needed inside double quotes, it must be escaped using a
backslash.

Strong quoting is achieved by surrounding single quotes ('') around the
character or sequence of characters to protect. Inside single quotes, nothing
is interpreted, it's the efficient way to quote regular expressions.

As a result, here is the matrix indicating how special characters can be
entered in different contexts (unprintable characters are replaced with their
name within angle brackets). Note that some characters that may only be
represented escaped have no possible representation inside single quotes,
hence its absence there:

# those are all strictly equivalent:
log-format %{+Q}o\ %t\ %s\ %{-Q}r
log-format "%{+Q}o %t %s %{-Q}r"
log-format '%{+Q}o %t %s %{-Q}r'
log-format "%{+Q}o %t"' %s %{-Q}r'
log-format "%{+Q}o %t"' %s'\ %{-Q}r

There is one particular case where a second level of quoting or escaping may be
necessary. Some keywords take arguments within parenthesis, sometimes delimited
by commas. These arguments are commonly integers or predefined words, but when
they are arbitrary strings, it may be required to perform a separate level of
escaping to disambiguate the characters that belong to the argument from the
characters that are used to delimit the arguments themselves. A pretty common
case is the "regsub" converter. It takes a regular expression in argument, and
if a closing parenthesis is needed inside, this one will require to have its
own quotes.

The keyword argument parser is exactly the same as the top-level one regarding
quotes, except that the \#, \$, and \xNN escapes are not processed. But what is
not always obvious is that the delimiters used inside must first be escaped or
quoted so that they are not resolved at the top level.

Let's take this example making use of the "regsub" converter which takes 3
arguments, one regular expression, one replacement string and one set of flags:

    # replace all occurrences of "foo" with "blah" in the path:
    http-request set-path %[path,regsub(foo,blah,g)]

Here no special quoting was necessary. But if now we want to replace either
"foo" or "bar" with "blah", we'll need the regular expression "(foo|bar)". We
cannot write:

    http-request set-path %[path,regsub((foo|bar),blah,g)]

because we would like the string to cut like this:

    http-request set-path %[path,regsub((foo|bar),blah,g)]
                                       |---------|----|-|
                                 arg1 _/         /    /
                                 arg2 __________/    /
                                 arg3 ______________/

but actually what is passed is a string between the opening and closing
parenthesis then garbage:

    http-request set-path %[path,regsub((foo|bar),blah,g)]
                                       |--------|--------|
                        arg1=(foo|bar _/        /
                    trailing garbage  _________/

The obvious solution here seems to be that the closing parenthesis needs to be
quoted, but alone this will not work, because as mentioned above, quotes are
processed by the top-level parser which will resolve them before processing
this word:

    http-request set-path %[path,regsub("(foo|bar)",blah,g)]
    ------------ -------- ----------------------------------
       word1       word2    word3=%[path,regsub((foo|bar),blah,g)]

So we didn't change anything for the argument parser at the second level which
still sees a truncated regular expression as the only argument, and garbage at
the end of the string. By escaping the quotes they will be passed unmodified to
the second level:

    http-request set-path %[path,regsub(\"(foo|bar)\",blah,g)]
    ------------ -------- ------------------------------------
       word1       word2    word3=%[path,regsub("(foo|bar)",blah,g)]
                                                |---------||----|-|
                                arg1=(foo|bar) _/          /    /
                                    arg2=blah  ___________/    /
                                        arg3=g _______________/

Another approach consists in using single quotes outside the whole string and
double quotes inside (so that the double quotes are not stripped again):

    http-request set-path '%[path,regsub("(foo|bar)",blah,g)]'
    ------------ --------  ----------------------------------
       word1       word2    word3=%[path,regsub("(foo|bar)",blah,g)]
                                                |---------||----|-|
                                arg1=(foo|bar) _/          /    /
                                          arg2 ___________/    /
                                          arg3 _______________/

But in this case it's important to note that delimiters embedded into the
higher level string remain pure characters and are not delimiters anymore. It
particularly means that spaces and tabs around commas are part of the string.
The example below is wrong on multiple points:

    http-request set-path '%[path, regsub("(foo|bar)", blah, g)]'
    ------------ --------  --------------------------------------
       word1       word2    word3=%[path, regsub("(foo|bar)", blah, g)]
                                        |--------|---------||-----|--|
                       converter=" regsub" _/        /         /   /
                                    arg1=(foo|bar) _/         /   /
                                     arg2=" blah" ___________/   /
                                        arg3=" g" ______________/

The single fact of surrounding commas with spaces resulted in the spaces being
part of the field itself, hence the converter " regsub" (starting with a
space), which won't be found and will trigger an error, but more subtly, the
replacement string " blah" will insert a space in the output. A good rule of
thumb is to never insert unneeded spaces inside expressions.

When using regular expressions, it can happen that the dollar ('$') character
appears in the expression or that a backslash ('\') is used in the replacement
string. In this case these ones will also be processed inside the double quotes
thus single quotes are preferred (or double escaping). Example:

    http-request set-path '%[path,regsub("^/(here)(/|$)","my/\1",g)]'
    ------------ --------  -----------------------------------------
       word1       word2    word3=%[path,regsub("^/(here)(/|$)","my/\1",g)]
                                                |-------------| |-----||-|
                              arg1=(here)(/|$) _/               /      /
                                    arg2=my/\1 ________________/      /
                                          arg3 ______________________/

Remember that backslashes are not escape characters within single quotes and
that the whole word above is already protected against them using the single
quotes. Conversely, if double quotes had been used around the whole expression,
single the dollar character and the backslashes would have been resolved at top
level, breaking the argument contents at the second level.

Unfortunately, since single quotes can't be escaped inside of strong quoting,
if you need to include single quotes in your argument, you will need to escape
or quote them twice. There are a few ways to do this:

    http-request set-var(txn.foo) str("\\'foo\\'")
    http-request set-var(txn.foo) str(\"\'foo\'\")
    http-request set-var(txn.foo) str(\\\'foo\\\')

When in doubt, simply do not use quotes anywhere, and start to place single or
double quotes around arguments that require a comma or a closing parenthesis,
and think about escaping these quotes using a backslash if the string contains
a dollar or a backslash. Again, this is pretty similar to what is used under
a Bourne shell when double-escaping a command passed to "eval". For API writers
the best is probably to place escaped quotes around each and every argument,
regardless of their contents. Users will probably find that using single quotes
around the whole expression and double quotes around each argument provides
more readable configurations.

HAProxy's configuration supports environment variables. Those variables are
interpreted only within double quotes. Variables are expanded during the
configuration parsing. Variable names must be preceded by a dollar ("$") and
optionally enclosed with braces ("{}") similarly to what is done in Bourne
shell. Variable names can contain alphanumerical characters or the character
underscore ("_") but should not start with a digit. If the variable contains a
list of several values separated by spaces, it can be expanded as individual
arguments by enclosing the variable with braces and appending the suffix '[*]'
before the closing brace. It is also possible to specify a default value to
use when the variable is not set, by appending that value after a dash '-'
next to the variable name. Note that the default value only replaces non
existing variables, not empty ones.

bind "fd@${FD_APP1}"

log "${LOCAL_SYSLOG-127.0.0.1}:514" local0 notice  # send to local server

user "$HAPROXY_USER"

Some variables are defined by HAProxy, they can be used in the configuration
file. These variables are listed in the matrix below, and they are classified
among four categories:

  * usable: the variable is accessible from the configuration, either to be
    resolved as-is, or used within conditional blocks or predicates to enable
    or disable this some configuration fragments, as described in section 2.4
    "Conditional blocks".

  * modifiable: the variable can be redefined or unset in the configuration via
    "setenv"/"unsetenv" keywords.

  * listed: the variable is listed in CLI's "show env" command output,
    described in section 9.3 "Unix Sockets commands" of the management guide.

There also two subcategories "master" and "worker", respectively marked 'M' and
'W' in the table below, showing the differences between the two processes when
HAProxy is launched in master-worker mode.

  * master: the variable is set and accessible from the master process. So, it
    will appear in the master CLI's "show env" output and it can be used in
    conditional blocks or directives to enable some special settings for the
    master (see examples in section 2.4 "Conditional blocks").

  * worker: the variable is set and accessible from the worker process. It will
    appear in the worker CLI's "show env" (or the master CLI's "@1 show env")
    and it may as well condition some worker process parameters (see examples
    from section 2.4 "Conditional blocks").

In standalone mode (without "-W" option nor the "master-worker" keyword) the
process behaves like a worker, except for variables "HAPROXY_MASTER_CLI" and
"HAPROXY_MWORKER" which are not defined.

Some variables are marked as not usable and not modifiable:

  * HAPROXY_CFGFILES
  * HAPROXY_MWORKER
  * HAPROXY_CLI
  * HAPROXY_MASTER_CLI
  * HAPROXY_LOCALPEER

Their values are undefined during configuration parsing, they are set later
during the initialization. So, it's recommended not to use these variables
within conditional blocks and not to reference them in the global section's
"setenv"/"resetenv"/"unsetenv" keywords.

The table below summaries the status of each variable for the different working
modes:

  +---------------------------+---------+------------+-----------+
  |          variable         | usable  | modifiable |  listed   |
  |                           +---------+------------+-----------+
  |                           |  M | W  |   M  |  W  |  M  |  W  |
  +---------------------------+----+----+------+-----+-----+-----+
  | HAPROXY_STARTUP_VERSION   |  X | X  |      |     |  X  |  X  |
  | HAPROXY_BRANCH            |  X | X  |      |     |  X  |  X  |
  | HAPROXY_CFGFILES          |    |    |      |     |  X  |  X  |
  | HAPROXY_MWORKER           |    |    |      |     |  X  |  X  |
  | HAPROXY_CLI               |    |    |      |     |     |  X  |
  | HAPROXY_MASTER_CLI        |    |    |      |     |  X  |     |
  | HAPROXY_LOCALPEER         |    | X  |      |     |     |  X  |
  | HAPROXY_HTTP_LOG_FMT      |    | X  |      |  X  |     |     |
  | HAPROXY_HTTP_CLF_LOG_FMT  |    | X  |      |  X  |     |     |
  | HAPROXY_HTTPS_LOG_FMT     |    | X  |      |  X  |     |     |
  | HAPROXY_TCP_LOG_FMT       |    | X  |      |  X  |     |     |
  | HAPROXY_TCP_CLF_LOG_FMT   |    | X  |      |  X  |     |     |
  | HAPROXY_KEYLOG_FC_LOG_FMT |    | X  |      |  X  |     |     |
  | HAPROXY_KEYLOG_BC_LOG_FMT |    | X  |      |  X  |     |     |
  +---------------------------+----+----+------+-----+-----+-----+

The variables in question are the following:

  * HAPROXY_LOCALPEER: defined at the startup of the process which contains the
    name of the local peer. (See "-L" in the management guide.)

  * HAPROXY_CFGFILES: list of the configuration files loaded by HAProxy,
    separated by semicolons. Can be useful in the case you specified a
    directory.

  * HAPROXY_HTTP_LOG_FMT: contains the value of the default HTTP log format as
    defined in section 8.2.3 "HTTP log format". It can be used to override the
    default log format without having to copy the whole original definition.

  * HAPROXY_HTTP_CLF_LOG_FMT: contains the value of the default HTTP CLF log
    format as defined in section 8.2.3 "HTTP log format". It can be used to
    override the default log format without having to copy the whole original
    definition.

# Add the rule that gave the final verdict to the log
log-format "${HAPROXY_TCP_LOG_FMT} lr=%[last_rule_file]:%[last_rule_line]"

  * HAPROXY_HTTPS_LOG_FMT: similar to HAPROXY_HTTP_LOG_FMT but for HTTPS log
    format as defined in section 8.2.4 "HTTPS log format".

  * HAPROXY_TCP_LOG_FMT: similar to HAPROXY_HTTP_LOG_FMT but for TCP log format
    as defined in section 8.2.2 "TCP log format".

  * HAPROXY_TCP_CLF_LOG_FMT: similar to HAPROXY_HTTP_CLF_LOG_FMT but for TCP
    CLF log format as defined in section 8.2.2 "TCP log format".

  * HAPROXY_KEYLOG_FC_LOG_FMT: contains the keylog format for the frontend
    (client-facing) TLS connection, with key entries separated by newlines so
    it might not be compatible with your syslog server. "tune.ssl.keylog on" is
    required.

  * HAPROXY_KEYLOG_BC_LOG_FMT: similar to HAPROXY_KEYLOG_FC_LOG_FMT but for the
    backend (server-facing) TLS connection. Key entries are separated by
    newlines so it might not be compatible with your syslog server.
    "tune.ssl.keylog on" is required.

  * HAPROXY_MWORKER: In master-worker mode, this variable is set to 1.

  * HAPROXY_CLI: configured listeners addresses of the stats socket of every
    processe, these addresses are separated by semicolons.

  * HAPROXY_MASTER_CLI: In master-worker mode, listeners addresses of the master
    CLI, separated by semicolons.

  * HAPROXY_STARTUP_VERSION: contains the version used to start, in master-
    worker mode this is the version which was used to start the master, even
    after updating the binary and reloading.

  * HAPROXY_BRANCH: contains the HAProxy branch version (such as "2.8"). It
    does not contain the full version number. It can be useful in case of
    migration if resources (such as maps or certificates) are in a path
    containing the branch number.

In addition, some pseudo-variables are internally resolved and may be used as
regular variables. Pseudo-variables always start with a dot ('.'), and are the
only ones where the dot is permitted. The current list of pseudo-variables is:

  * .FILE: the name of the configuration file currently being parsed.

  * .LINE: the line number of the configuration file currently being parsed,
    starting at one.

  * .SECTION: the name of the section currently being parsed, or its type if
    the section doesn't have a name (e.g. "global"), or an empty string before
    the first section.

These variables are resolved at the location where they are parsed. For example
if a ".LINE" variable is used in a "log-format" directive located in a defaults
section, its line number will be resolved before parsing and compiling the
"log-format" directive, so this same line number will be reused by subsequent
proxies.

This way it is possible to emit information to help locate a rule in variables,
logs, error statuses, health checks, header values, or even to use line numbers
to name some config objects like servers for example.

It may sometimes be convenient to be able to conditionally enable or disable
some arbitrary parts of the configuration, for example to enable/disable SSL or
ciphers, enable or disable some pre-production listeners without modifying the
configuration, or adjust the configuration's syntax to support two distinct
versions of HAProxy during a migration.. HAProxy brings a set of nestable
preprocessor-like directives which allow to integrate or ignore some blocks of
text. These directives must be placed on their own line and they act on the
lines that follow them. Two of them support an expression, the other ones only
switch to an alternate block or end a current level. The 4 following directives
are defined to form conditional blocks:

  - .if <condition>
  - .elif <condition>
  - .else
  - .endif

The ".if" directive nests a new level, ".elif" stays at the same level, ".else"
as well, and ".endif" closes a level. Each ".if" must be terminated by a
matching ".endif". The ".elif" may only be placed after ".if" or ".elif", and
there is no limit to the number of ".elif" that may be chained. There may be
only one ".else" per ".if" and it must always be after the ".if" or the last
".elif" of a block.

Comments may be placed on the same line if needed after a '#', they will be
ignored. The directives are tokenized like other configuration directives, and
as such it is possible to use environment variables in conditions.

Conditions can also be evaluated on startup with the -cc parameter.
See "3. Starting HAProxy" in the management doc.

The conditions are either an empty string (which then returns false), or an
expression made of any combination of:

  - the integer zero ('0'), always returns "false"
  - a non-nul integer (e.g. '1'), always returns "true".
  - a predicate optionally followed by argument(s) in parenthesis.
  - a condition placed between a pair of parenthesis '(' and ')'
  - an exclamation mark ('!') preceding any of the non-empty elements above,
    and which will negate its status.
  - expressions combined with a logical AND ('&&'), which will be evaluated
    from left to right until one returns false
  - expressions combined with a logical OR ('||'), which will be evaluated
    from right to left until one returns true

The same line tokenizer and argument parser are used as for the rest of the
configuration language. Words are split around consecutive series of one or
more unquoted spaces or tabs, and are reassembled together using a single space
to delimit them before evaluation, in order to save the user from having to
quote the entire line. But this also means that spaces surrounding commas or
parenthesis are definitely part of the value, which is not always expected.
For example, the expression below:

   .if defined( HAPROXY_MWORKER )

will test for the existence of variable " HAPROXY_MWORKER " (with spaces),
and this one:

   .if streq("$ENABLE_SSL",     1)

will compare the environment variable "ENABLE_SSL" to the value " 1" (with a
single leading space). The reason is the line is first split into words like
this:

   .if streq("$ENABLE_SSL",     1)
  |---|--------------------|   |--|
    1           2               3

then the weak quoting is applied and environment variable "$ENABLE_SSL" is
resolved (let's say for example that ENABLE_SSL=0), and finally the words are
reassembled into a single string by placing a single space between the words:

   .if streq(0, 1)
  |---|-------|--|
    1     2     3

and only then it is parsed as a single expression. The space that was inserted
between the comma and "1" is still part of the argument value, making this
argument " 1":

   .if streq(0, 1)
  |---|-----|-|--|
    \    \    \  \_ argument2: " 1"
     \    \    \___ argument1: "0"
      \    \_______ function: "streq"
       \___________ directive: ".if"

It's visible here that even if ENABLE_SSL had been equal to "1", it wouldn't
have matched " 1" since the string would differ by one space.

Note: as explained in section "2.2. Quoting and escaping", a good rule of thumb
      is to never insert unneeded spaces inside expressions.

Note that like in other languages, the AND operator has precedence over the OR
operator, so that "A && B || C && D" evalues as "(A && B) || (C && D)".

The list of currently supported predicates is the following:

  - awslc_api_atleast(<ver>): returns true if the current awslc API number
                            is at least as recent as <ver> otherwise false.

awslc_api_atleast(35)

- awslc_api_before(<ver>): returns true if the current awslc API number
                          is strictly older than <ver> otherwise false.

awslc_api_before(26)

- defined(<name>)       : returns true if an environment variable <name>
                          exists, regardless of its contents

- feature(<name>)       : returns true if feature <name> is listed as present
                          in the features list reported by "haproxy -vv"
                          (which means a <name> appears after a '+')

- openssl_version_atleast(<ver>) : returns true if the current openssl
                          version is at least as recent as <ver> otherwise
                          false.
                          Libraries like LibreSSL, AWS-LC and WolfSSL also
                          provide a pseudo OpenSSL version.

ssllib_name_startswith(OpenSSL) && openssl_version_atleast(1.1.1)

- openssl_version_before(<ver>) : returns true if the current openssl
                          version is strictly older than <ver> otherwise
                          false.
                          Libraries like LibreSSL, AWS-LC and WolfSSL also
                          provide a pseudo OpenSSL version.

openssl_version_before(3.5.0)

- ssllib_name_startswith(<name>)  : return true if the SSL library name
                          HAProxy was linked with, starts with <name>.

ssllib_name_startswith(wolfSSL)

- streq(<str1>,<str2>)  : returns true only if the two strings are equal
- strneq(<str1>,<str2>) : returns true only if the two strings differ
- strstr(<str1>,<str2>) : returns true only if the second string is found in
                          the first one.

- version_atleast(<ver>): returns true if the current haproxy version is
                          at least as recent as <ver> otherwise false. The
                          version syntax is the same as shown by "haproxy -v"
                          and missing components are assumed as being zero.

- version_before(<ver>) : returns true if the current haproxy version is
                          strictly older than <ver> otherwise false. The
                          version syntax is the same as shown by "haproxy -v"
                          and missing components are assumed as being zero.

- enabled(<opt>)        : returns true if the option <opt> is enabled at
                          run-time. Only a subset of options are supported:
                              POLL, EPOLL, KQUEUE, EVPORTS, SPLICE,
                              GETADDRINFO, REUSEPORT, FAST-FORWARD,
                              SERVER-SSL-VERIFY-NONE

# 1. HAPROXY_MWORKER variable is set automatically by HAProxy in master and
# in worker process environments (see HAProxy variables matrix from
# 2.3. Environment variables). Its presence enables an additional listener.

global
  master-worker

.if defined(HAPROXY_MWORKER)
    listen mwcli_px
       bind :1111
       ...
.endif

# 2. HAPROXY_BRANCH is set automatically by HAProxy in master and in worker
# process environments (see HAProxy variables matrix from 2.3. Environment
# variables). We check HAPROXY_BRANCH value and conditionally enable
# mworker-max-reloads parameter.

global
  master-worker

.if streq("$HAPROXY_BRANCH",3.1)
     mworker-max-reloads 5
.endif

# 3. Some arbitrary environment variables are set by user in the global
# section. If HAProxy is started in master-worker mode, they are presented in
# master and in worker process environments. We check values of these
# variables and conditionally enable ports 80 and 443. Environment variables
# checks can be mixed with features and version checks.

global
  setenv WITH_SSL yes
  unsetenv SSL_ONLY

.if strneq("$SSL_ONLY",yes)
       bind :80
.endif

.if streq("$WITH_SSL",yes)
  .if feature(OPENSSL)
       bind :443 ssl crt ...
  .endif
.endif

.if feature(OPENSSL) && (streq("$WITH_SSL",yes) || streq("$SSL_ONLY",yes))
       bind :443 ssl crt ...
.endif

.if version_atleast(2.4-dev19)
    profiling.memory on
.endif

.if !feature(OPENSSL)
    .alert "SSL support is mandatory"
.endif

Four other directives are provided to report some status:

  - .diag "message"    : emit this message only when in diagnostic mode (-dD)
  - .notice "message"  : emit this message at level NOTICE
  - .warning "message" : emit this message at level WARNING
  - .alert "message"   : emit this message at level ALERT

Messages emitted at level WARNING may cause the process to fail to start if
"zero-warning" is enabled. Messages emitted at level ALERT will always cause a
fatal error. These can be used to detect some inappropriate conditions and
provide advice to the user.

.if "${A}"
  .if "${B}"
     .notice "A=1, B=1"
  .elif "${C}"
     .notice "A=1, B=0, C=1"
  .elif "${D}"
     .warning "A=1, B=0, C=0, D=1"
  .else
     .alert "A=1, B=0, C=0, D=0"
  .endif
.else
     .notice "A=0"
.endif

.diag "WTA/2021-05-07: replace 'redirect' with 'return' after switch to 2.4"
      http-request redirect location /goaway if ABUSE

Some parameters involve values representing time, such as timeouts. These
values are generally expressed in milliseconds (unless explicitly stated
otherwise) but may be expressed in any other unit by suffixing the unit to the
numeric value. It is important to consider this because it will not be repeated
for every keyword. Supported units are :

  - us : microseconds. 1 microsecond = 1/1000000 second
  - ms : milliseconds. 1 millisecond = 1/1000 second. This is the default.
  - s  : seconds. 1s = 1000ms
  - m  : minutes. 1m = 60s = 60000ms
  - h  : hours.   1h = 60m = 3600s = 3600000ms
  - d  : days.    1d = 24h = 1440m = 86400s = 86400000ms

Some parameters involve values representing size, such as bandwidth limits.
These values are generally expressed in bytes (unless explicitly stated
otherwise) but may be expressed in any other unit by suffixing the unit to the
numeric value. It is important to consider this because it will not be repeated
for every keyword. Supported units are case insensitive :

  - k : kilobytes. 1 kilobyte = 1024 bytes
  - m : megabytes. 1 megabyte = 1048576 bytes
  - g : gigabytes. 1 gigabyte = 1073741824 bytes

Both time and size formats require integers, decimal notation is not allowed.

It is possible to use a list of pattern for maps or ACLs. A list of pattern is
identified by its name and may be used at different places in the
configuration. List of pattern are split on three categories depending on
the name format:

  * Lists of pattern based on regular files: It is the default case. The
    filename, absolute or relative, is used as name. The file must exist
    otherwise an error is triggered. But it may be empty. The "file@" prefix
    may also be specified but it is not part of the name identifying the
    list. A filename, with or without the prefix, references the same list of
    pattern.

  * Lists of pattern based on optional files: The filename must be preceded by
    "opt@" prefix. The file existence is optional. If the file exists, its
    content is loaded but no error is reported if not. The prefix is not part
    of the name identifying the list. It means, for a given filename, Optional
    files and regular files reference the same list of pattern.

  * Lists of pattern based on virtual files: The name is just an identifier. It
    is not a reference to any file. "virt@" prefix must be used. It is part of
    the name. Thus it cannot be mixed with other kind of lists.

Virtual files are useful when patterns are fully dynamically managed with no
patterns on startup and on reload. Optional files may be used under the same
conditions. But patterns can be dumped in the file, via an external script based
on the "show map" CLI command for instance. This way, it is possible to keep
patterns on reload.

Note: Even if it is unlikely, it means no regular file starting with "file@",
      "opt@" or "virt@" can be loaded, except by adding "./" explicitly in
      front of the filename (for instance "file@./virt@map").

In HAProxy configuration, variables can be used in sample fetch functions,
converters, log-format strings or TCP/HTTP actions. Process-wide variables can
be defined, globally accessible for the whole life of the process. Some others
have a shorter lifespan. Variables are similar to those found in shell
scripts. It is a symbolic name for a chunk of memory. The variables size is not
limited and is dynamically allocated. So they must be used with caution,
especially for an intensive usage. However, it is possible to limit the maximum
amount of memory used by the variables by setting "tune.vars" global parameters.

Variables must be designated using the format "<scope>.<name>". The <scope> is
a single word indicating the life time of the variable. The <name> part, inside
a scope, may only contain characters 'a-z', 'A-Z', '0-9' and '_'. It is unique
in this scope but the same name in different scopes can be used and refers to
different variables. Supported scopes are:

  * proc  : for variables known during the whole process lifespan and globally
            accessible. "proc" variables can be manipulated from the CLI using
            "get var" and "set var" commands. They can also be set from
            "global" sections via "set-var
This keyword is available in sections :
Process management and security
Alphabetically sorted actions reference
Converters" and "set-var-fmt
This keyword is available in sections :
Process management and security
Alphabetically sorted actions reference" directives.

  * sess  : for variables known during the whole lifespan of a session. "sess"
            variables are private to a session, not visbile from outside it and
            not shared with other sessions.

  * txn   : for variables known during the whole lifespan of a transaction. "txn"
            variables are private to a stream, not visible from outside it and
            not shared with other streams.

  * req   : for variables known during the request processing for a specific
            stream. "req" variables are visible from the stream creation and
            until the first server connection attempt. They are private to a
            stream, not visible from outside it and not shared with other
            streams. There is no overlap at all between "req" and "res"
            variables.

  * res   : for variables known during the response processing for a specific
            stream. "res" variables are visible from the first server
            connection attempt and until the stream destruction. They are
            private to a stream, not visible from outside it and not shared
            with other streams. There is no overlap at all between "req" and
            "res" variables.

  * check : for variables known during a health-check execution. "check"
            variables are private to a health-check, not visible from outside
            it and are not shared with other health-checks. They can be set
            using dedicated "tcp-check" or "http-check
This keyword is available in sections :
Healthchecks
Alphabetically sorted keywords reference" directives.

Depending on the context, extra scopes referencing the parent of a current
stream can be used:

  * psess : same as "sess" but using the session of the parent stream, if any.

  * ptxn  : same as "txn" but using the transaction of the parent stream, if
            any.

  * preq  : same as "req" but using the parent stream, if any. "preq"
            variables are only accessible during request processing of the
            parent stream.

  * pres  : same as "res" but using the parent stream, if any. "pres"
            variables are only accessible during response processing of the
            parent stream.

Scopes referencing the parent stream are usable from the moment it is defined.
Most of time, there is no parent stream. But, if applicable, this will be
explicitly specified. For now, it is only possible to retrieve the value of
variables defined in a scope of the parent stream. It is not possible to set
nor unset such variables. Usually a child stream performs some processing for
the parent at a precise moment and prevents it from making progress until the
operation it does is completed. This means that the parent may be stopped in
the middle of a request processing or a response processing for example. As
such, certain scopes will not be available from the child stream. For example
if a request is subject to some analysis performed by a child stream, this
child stream will not find any variable in the "pres" scope since the parent is
not processing a response, hence doesn't have any variables in its "res" scope.

The content of a variable is the result of the evaluation of a sample fetch
expression and it inherits of the output type of this expression. It is
important when the variable is used because its type must be compatible with
its usage. For instance a variable containing a string used in "add()"
converter must be convertible to a valid integer to succeed. It is especially
true when variables are compared to static value. The right matching method
must be used.

Several statements as "bind, "server
This keyword is available in sections :
Peers declaration
Rings
Alphabetically sorted keywords reference", "nameserver" and "log
This keyword is available in sections :
Peers declaration
Log forwarding
Process management and security
Alphabetically sorted keywords reference" requires an
address.

This address can be a host name, an IPv4 address, an IPv6 address, or '*'.
The '*' is equal to the special address "0.0.0.0" and can be used, in the case
of "bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference" or "dgram-bind" to listen on all IPv4 of the system.The IPv6
equivalent is '::'.

Depending of the statement, a port or port range follows the IP address. This
is mandatory on 'bind' statement, optional on 'server'.

This address can also begin with a slash '/'. It is considered as the "unix"
family, and '/' and following characters must be present the path.

Default socket type or transport method "datagram" or "stream" depends on the
configuration statement showing the address. Indeed, 'bind' and 'server' will
use a "stream" socket type by default whereas 'log', 'nameserver' or
'dgram-bind' will use a "datagram".

Optionally, a prefix could be used to force the address family and/or the
socket type and the transport method.

'abns@<name>' following <name> is an abstract namespace (Linux only).

'abnsz@<name>' following <name> is a zero-terminated abstract namespace
               (Linux only).

'fd@<n>'      following address is a file descriptor <n> inherited from the
              parent. The fd must be bound and may or may not already be
              listening.

'ip@<address>[:port1[-port2]]' following <address> is considered as an IPv4 or
                               IPv6 address depending on the syntax. Depending
                               on the statement using this address, a port or
                               a port range may or must be specified.

'ipv4@<address>[:port1[-port2]]' following <address> is always considered as
                                 an IPv4 address. Depending on the statement
                                 using this address, a port or a port range
                                 may or must be specified.

'ipv6@<address>[:port1[-port2]]' following <address> is always considered as
                                 an IPv6 address. Depending on the statement
                                 using this address, a port or a port range
                                 may or must be specified.

'sockpair@<n>' following address is the file descriptor of a connected unix
               socket or of a socketpair. During a connection, the initiator
               creates a pair of connected sockets, and passes one of them
               over the FD to the other end. The listener waits to receive
               the FD from the unix socket and uses it as if it were the FD
               of an accept(). Should be used carefully.

               Bugs: This protocol is known to be unreliable on macOS because
               of an issue in the macOS sendmsg(2) implementation. The
               connection might not be accepted correctly.


'unix@<path>'  following string is considered as a UNIX socket <path>. this
               prefix is useful to declare an UNIX socket path which don't
               start by slash '/'.

Previous "Address family prefixes" can also be prefixed to force the socket
type and the transport method. The default depends of the statement using
this address but in some cases the user may force it to a different one.
This is the case for "log
This keyword is available in sections :
Peers declaration
Log forwarding
Process management and security
Alphabetically sorted keywords reference" statement where the default is syslog over UDP
but we could force to use syslog over TCP.

Those prefixes were designed for internal purpose and users should instead use
use aliases of the next section "2.9.3 Protocol prefixes". However these can
sometimes be convenient, for example in combination with inherited sockets
known by their file descriptor number, in which case the address family is "fd"
and the socket type must be declared.

If users need one those prefixes to perform what they expect because
they can not configure the same using the protocol prefixes, they should
report this to the maintainers.

'stream+<family>@<address>' forces socket type and transport method
                            to "stream"

'dgram+<family>@<address>'  forces socket type and transport method
                            to "datagram".

'quic+<family>@<address>'   forces socket type to "datagram" and transport
                            method to "stream".

'quic4@<address>[:port1[-port2]]' following <address> is always considered as
                                  an IPv4 address but socket type is forced to
                                  "datagram" and the transport method is forced
                                  to "stream". Depending on the statement using
                                  this address, a UDP port or port range can or
                                  must be specified. It is equivalent to
                                  "quic+ipv4@".

'quic6@<address>[:port1[-port2]]' following <address> is always considered as
                                  an IPv6 address but socket type is forced to
                                  "datagram" and the transport method is forced
                                  to "stream". Depending on the statement using
                                  this address, a UDP port or port range can or
                                  must be specified. It is equivalent to
                                  "quic+ipv6@".

'tcp@<address>[:port1[-port2]]' following <address> is considered as an IPv4
                                or IPv6 address depending of the syntax but
                                socket type and transport method is forced to
                                "stream". Depending on the statement using
                                this address, a port or a port range can or
                                must be specified. It is considered as an alias
                                of 'stream+ip@'.

'tcp4@<address>[:port1[-port2]]' following <address> is always considered as
                                 an IPv4 address but socket type and transport
                                 method is forced to "stream". Depending on the
                                 statement using this address, a port or port
                                 range can or must be specified.
                                 It is considered as an alias of 'stream+ipv4@'.

'tcp6@<address>[:port1[-port2]]' following <address> is always considered as
                                 an IPv6 address but socket type and transport
                                 method is forced to "stream". Depending on the
                                 statement using this address, a port or port
                                 range can or must be specified.
                                 It is considered as an alias of 'stream+ipv4@'.

'mptcp@<address>[:port1[-port2]]' following <address> is considered as an IPv4
                                  or IPv6 address depending of the syntax but
                                  socket type and transport method is forced to
                                  "stream", with the MPTCP protocol. Depending
                                  on the statement using this address, a port or
                                  a port range can or must be specified.

'mptcp4@<address>[:port1[-port2]]' following <address> is always considered as
                                   an IPv4 address but socket type and transport
                                   method is forced to "stream", with the MPTCP
                                   protocol. Depending on the statement using
                                   this address, a port or port range can or
                                   must be specified.

'mptcp6@<address>[:port1[-port2]]' following <address> is always considered as
                                   an IPv6 address but socket type and transport
                                   method is forced to "stream", with the MPTCP
                                   protocol. Depending on the statement using
                                   this address, a port or port range can or
                                   must be specified.

'udp@<address>[:port1[-port2]]' following <address> is considered as an IPv4
                                or IPv6 address depending of the syntax but
                                socket type and transport method is forced to
                                "datagram". Depending on the statement using
                                this address, a port or a port range can or
                                must be specified. It is considered as an alias
                                of 'dgram+ip@'.

'udp4@<address>[:port1[-port2]]' following <address> is always considered as
                                 an IPv4 address but socket type and transport
                                 method is forced to "datagram". Depending on
                                 the statement using this address, a port or
                                 port range can or must be specified.
                                 It is considered as an alias of 'dgram+ipv4@'.

'udp6@<address>[:port1[-port2]]' following <address> is always considered as
                                 an IPv6 address but socket type and transport
                                 method is forced to "datagram". Depending on
                                 the statement using this address, a port or
                                 port range can or must be specified.
                                 It is considered as an alias of 'dgram+ipv4@'.

'uxdg@<path>'    following string is considered as a unix socket <path> but
                 transport method is forced to "datagram". It is considered as
                 an alias of 'dgram+unix@'.

'uxst@<path>'    following string is considered as a unix socket <path> but
                 transport method is forced to "stream". It is considered as
                 an alias of 'stream+unix@'.

In future versions, other prefixes could be used to specify protocols like
QUIC which proposes stream transport based on socket of type "datagram".

    # Simple configuration for an HTTP proxy listening on port 80 on all
    # interfaces and forwarding requests to a single backend "servers" with a
    # single server "server1" listening on 127.0.0.1:8000
    global
        daemon
        maxconn 256

    defaults
        mode http
        timeout connect 5000ms
        timeout client 50000ms
        timeout server 50000ms

    frontend http-in
        bind *:80
        default_backend servers

    backend servers
        server server1 127.0.0.1:8000 maxconn 32


    # The same configuration defined with a single listen block. Shorter but
    # less expressive, especially in HTTP mode.
    global
        daemon
        maxconn 256

    defaults
        mode http
        timeout connect 5000ms
        timeout client 50000ms
        timeout server 50000ms

    listen http-in
        bind *:80
        server server1 127.0.0.1:8000 maxconn 32


Assuming haproxy is in $PATH, test these configurations in a shell with:

    $ sudo haproxy -f configuration.conf -c

Parameters in the "global" section are process-wide and often OS-specific. They
are generally set once for all and do not need being changed once correct. Some
of them have command-line equivalents.

The following keywords are supported in the "global" section :

 * Process management and security
   - 51degrees-allow-unmatched
   - 51degrees-cache-size
   - 51degrees-data-file
   - 51degrees-difference
   - 51degrees-drift
   - 51degrees-property-name-list
   - 51degrees-property-separator
   - 51degrees-use-performance-graph
   - 51degrees-use-predictive-graph
   - ca-base
   - chroot
   - cluster-secret
   - cpu-affinity
   - cpu-map
   - cpu-policy
   - cpu-set
   - crt-base
   - daemon
   - default-path
   - description
   - deviceatlas-json-file
   - deviceatlas-log-level
   - deviceatlas-properties-cookie
   - deviceatlas-separator
   - dns-accept-family
   - expose-deprecated-directives
   - expose-experimental-directives
   - external-check
   - fd-hard-limit
   - gid
   - grace
   - group
   - h1-accept-payload-with-any-method
   - h1-case-adjust
   - h1-case-adjust-file
   - h1-do-not-close-on-insecure-transfer-encoding
   - h2-workaround-bogus-websocket-clients
   - hard-stop-after
   - harden.reject-privileged-ports.tcp
   - harden.reject-privileged-ports.quic
   - insecure-fork-wanted
   - insecure-setuid-wanted
   - issuers-chain-path
   - jwt.decrypt_alg_list
   - jwt.decrypt_enc_list
   - key-base
   - limited-quic
   - localpeer
   - log
   - log-send-hostname
   - log-tag
   - lua-load
   - lua-load-per-thread
   - lua-prepend-path
   - max-threads-per-group
   - mworker-max-reloads
   - nbthread
   - node
   - numa-cpu-mapping
   - ocsp-update.disable
   - ocsp-update.maxdelay
   - ocsp-update.mindelay
   - ocsp-update.httpproxy
   - ocsp-update.mode
   - pidfile
   - pp2-never-send-local
   - presetenv
   - prealloc-fd
   - resetenv
   - set-dumpable
   - set-var
   - setenv
   - ssl-default-bind-ciphers
   - ssl-default-bind-ciphersuites
   - ssl-default-bind-client-sigalgs
   - ssl-default-bind-curves
   - ssl-default-bind-options
   - ssl-default-bind-sigalgs
   - ssl-default-server-ciphers
   - ssl-default-server-ciphersuites
   - ssl-default-server-client-sigalgs
   - ssl-default-server-curves
   - ssl-default-server-options
   - ssl-default-server-sigalgs
   - ssl-dh-param-file
   - ssl-propquery
   - ssl-provider
   - ssl-provider-path
   - ssl-security-level
   - ssl-server-verify
   - ssl-skip-self-issued-ca
   - stats
   - stats-file
   - strict-limits
   - uid
   - ulimit-n
   - unix-bind
   - unsetenv
   - user
   - wurfl-cache-size
   - wurfl-data-file
   - wurfl-information-list
   - wurfl-information-list-separator

 * Performance tuning
   - busy-polling
   - max-spread-checks
   - maxcompcpuusage
   - maxcomprate
   - maxconn
   - maxconnrate
   - maxpipes
   - maxsessrate
   - maxsslconn
   - maxsslrate
   - maxzlibmem
   - no-memory-trimming
   - noepoll
   - noevports
   - nogetaddrinfo
   - nokqueue
   - noktls
   - nopoll
   - noreuseport
   - nosplice
   - profiling.memory
   - profiling.tasks
   - server-state-base
   - server-state-file
   - spread-checks
   - ssl-engine
   - ssl-mode-async
   - tune.applet.zero-copy-forwarding
   - tune.buffers.limit
   - tune.buffers.reserve
   - tune.bufsize
   - tune.bufsize.large
   - tune.bufsize.small
   - tune.cli.max-payload-size
   - tune.comp.maxlevel
   - tune.defaults.purge
   - tune.disable-fast-forward
   - tune.disable-zero-copy-forwarding
   - tune.epoll.mask-events
   - tune.events.max-events-at-once
   - tune.fail-alloc
   - tune.fd.edge-triggered
   - tune.h1.be.glitches-threshold
   - tune.h1.fe.glitches-threshold
   - tune.h1.zero-copy-fwd-recv
   - tune.h1.zero-copy-fwd-send
   - tune.h2.be.glitches-threshold
   - tune.h2.be.initial-window-size
   - tune.h2.be.max-concurrent-streams
   - tune.h2.be.max-frames-at-once
   - tune.h2.be.rxbuf
   - tune.h2.fe.glitches-threshold
   - tune.h2.fe.initial-window-size
   - tune.h2.fe.max-concurrent-streams
   - tune.h2.fe.max-frames-at-once
   - tune.h2.fe.max-rst-at-once
   - tune.h2.fe.max-total-streams
   - tune.h2.fe.rxbuf
   - tune.h2.header-table-size
   - tune.h2.initial-window-size
   - tune.h2.max-concurrent-streams
   - tune.h2.max-frame-size
   - tune.h2.zero-copy-fwd-send
   - tune.http.cookielen
   - tune.http.logurilen
   - tune.http.maxhdr
   - tune.idle-pool.shared
   - tune.idletimer
   - tune.lua.bool-sample-conversion
   - tune.lua.burst-timeout
   - tune.lua.forced-yield
   - tune.lua.log.loggers
   - tune.lua.log.stderr
   - tune.lua.maxmem
   - tune.lua.openlibs
   - tune.lua.service-timeout
   - tune.lua.session-timeout
   - tune.lua.task-timeout
   - tune.max-checks-per-thread
   - tune.maxaccept
   - tune.maxpollevents
   - tune.maxrewrite
   - tune.max-rules-at-once
   - tune.memory.hot-size
   - tune.pattern.cache-size
   - tune.peers.max-updates-at-once
   - tune.pipesize
   - tune.pool-high-fd-ratio
   - tune.pool-low-fd-ratio
   - tune.pt.zero-copy-forwarding
   - tune.quic.be.cc.cubic-min-losses
   - tune.quic.be.cc.hystart
   - tune.quic.be.cc.max-frame-loss
   - tune.quic.be.cc.max-win-size
   - tune.quic.be.cc.reorder-ratio
   - tune.quic.be.max-idle-timeout
   - tune.quic.be.sec.glitches-threshold
   - tune.quic.be.stream.data-ratio
   - tune.quic.be.stream.max-concurrent
   - tune.quic.be.stream.rxbuf
   - tune.quic.be.tx.pacing
   - tune.quic.be.tx.udp-gso
   - tune.quic.cc.cubic.min-losses (deprecated)
   - tune.quic.cc-hystart (deprecated)
   - tune.quic.disable-tx-pacing (deprecated)
   - tune.quic.disable-udp-gso (deprecated)
   - tune.quic.fe.cc.cubic-min-losses
   - tune.quic.fe.cc.hystart
   - tune.quic.fe.cc.max-frame-loss
   - tune.quic.fe.cc.max-win-size
   - tune.quic.fe.cc.reorder-ratio
   - tune.quic.fe.max-idle-timeout
   - tune.quic.fe.sec.glitches-threshold
   - tune.quic.fe.sec.retry-threshold
   - tune.quic.fe.sock-per-conn
   - tune.quic.fe.stream.data-ratio
   - tune.quic.fe.stream.max-concurrent
   - tune.quic.fe.stream.max-total
   - tune.quic.fe.stream.rxbuf
   - tune.quic.fe.tx.pacing
   - tune.quic.fe.tx.udp-gso
   - tune.quic.frontend.max-data-size (deprecated)
   - tune.quic.frontend.max-idle-timeout (deprecated)
   - tune.quic.frontend.max-streams-bidi (deprecated)
   - tune.quic.frontend.max-tx-mem (deprecated)
   - tune.quic.frontend.stream-data-ratio (deprecated)
   - tune.quic.frontend.default-max-window-size (deprecated)
   - tune.quic.listen
   - tune.quic.max-frame-loss (deprecated)
   - tune.quic.mem.tx-max
   - tune.quic.reorder-ratio (deprecated)
   - tune.quic.retry-threshold (deprecated)
   - tune.quic.socket-owner (deprecated)
   - tune.quic.zero-copy-fwd-send
   - tune.renice.runtime
   - tune.renice.startup
   - tune.rcvbuf.backend
   - tune.rcvbuf.client
   - tune.rcvbuf.frontend
   - tune.rcvbuf.server
   - tune.recv_enough
   - tune.ring.queues
   - tune.runqueue-depth
   - tune.sched.low-latency
   - tune.sndbuf.backend
   - tune.sndbuf.client
   - tune.sndbuf.frontend
   - tune.sndbuf.server
   - tune.streams-elasticity
   - tune.stick-counters
   - tune.ssl.cachesize
   - tune.ssl.capture-buffer-size
   - tune.ssl.capture-cipherlist-size (deprecated)
   - tune.ssl.certificate-compression
   - tune.ssl.default-dh-param
   - tune.ssl.force-private-cache
   - tune.ssl.hard-maxrecord
   - tune.ssl.keylog
   - tune.ssl.keyupdate-rate-limit
   - tune.ssl.lifetime
   - tune.ssl.maxrecord
   - tune.ssl.ssl-ctx-cache-size
   - tune.ssl.ocsp-update.maxdelay (deprecated)
   - tune.ssl.ocsp-update.mindelay (deprecated)
   - tune.takeover-other-tg-connections
   - tune.vars.global-max-size
   - tune.vars.proc-max-size
   - tune.vars.reqres-max-size
   - tune.vars.sess-max-size
   - tune.vars.txn-max-size
   - tune.zlib.memlevel
   - tune.zlib.windowsize

 * Debugging
   - anonkey
   - debug.counters
   - force-cfg-parser-pause
   - quiet
   - warn-blocked-traffic-after
   - zero-warning

 * HTTPClient
   - httpclient.resolvers.disabled
   - httpclient.resolvers.id
   - httpclient.resolvers.prefer
   - httpclient.retries
   - httpclient.ssl.ca-file
   - httpclient.ssl.verify
   - httpclient.timeout.connect

The path of the 51Degrees data file to provide device detection services. The
file should be unzipped and accessible by HAProxy with relevant permissions.

Please note that this option is only available when HAProxy has been
compiled with USE_51DEGREES.

A list of 51Degrees property names to be load from the dataset. A full list
of names is available on the 51Degrees website:
https://51degrees.com/resources/property-dictionary

Please note that this option is only available when HAProxy has been
compiled with USE_51DEGREES.

A char that will be appended to every property value in a response header
containing 51Degrees results. If not set that will be set as ','.

Please note that this option is only available when HAProxy has been
compiled with USE_51DEGREES.

Sets the size of the 51Degrees converter cache to <number> entries. This
is an LRU cache which reminds previous device detections and their results.
By default, this cache is disabled.

Please note that this option is only available when HAProxy has been
compiled with USE_51DEGREES.

Enables ('on') or disables ('off') the use of the performance graph in
the detection process. The default value depends on 51Degrees library.

Please note that this option is only available when HAProxy has been
compiled with USE_51DEGREES and 51DEGREES_VER=4.

Enables ('on') or disables ('off') the use of the predictive graph in
the detection process. The default value depends on 51Degrees library.

Please note that this option is only available when HAProxy has been
compiled with USE_51DEGREES and 51DEGREES_VER=4.

Sets the drift value that a detection can allow.

Please note that this option is only available when HAProxy has been
compiled with USE_51DEGREES and 51DEGREES_VER=4.

Sets the difference value that a detection can allow.

Please note that this option is only available when HAProxy has been
compiled with USE_51DEGREES and 51DEGREES_VER=4.

Enables ('on') or disables ('off') the use of unmatched nodes in the
detection process. The default value depends on 51Degrees library.

Please note that this option is only available when HAProxy has been
compiled with USE_51DEGREES and 51DEGREES_VER=4.

Enable or disable the ACME scheduler.

The ACME scheduler starts at HAProxy startup, it will loop over the
certificates and start an ACME renewal task when the notAfter value is past
curtime + (notAfter - notBefore) / 12, or 7 days if notBefore is not defined.
The scheduler will then sleep and wakeup after 12 hours.

The default value is "auto".

Assigns a default directory to fetch SSL CA certificates and CRLs from when a
relative path is used with "ca-file
This keyword is available in sections :
Bind options
Server and default-server options", "ca-verify-file" or "crl-file
This keyword is available in sections :
Bind options
Server and default-server options"
directives. Absolute locations specified in "ca-file
This keyword is available in sections :
Bind options
Server and default-server options", "ca-verify-file" and
"crl-file
This keyword is available in sections :
Bind options
Server and default-server options" prevail and ignore "ca-base".

Changes current directory to <jail dir> and performs a chroot() there before
dropping privileges. This increases the security level in case an unknown
vulnerability would be exploited, since it would make it very hard for the
attacker to exploit the system. It is important to ensure that <jail dir>
is both empty and non-writable to anyone. When the process is started with
superuser privileges, the chroot() is performed directly. On Linux, when
started unprivileged, haproxy attempts to perform it from inside a new
user namespace created with unshare(CLONE_NEWUSER); if that mechanism is
unavailable the chroot() will fail with the usual error.

As a special case, <jail dir> may be set to "auto", in which case haproxy
creates an anonymous temporary directory, unlinks it, and chroots into it.
The resulting jail has no name in the filesystem and is empty and read-only,
removing the need to prepare a dedicated jail directory.

When starting with superuser privileges, a warning will be displayed if no
chroot is used, in order to encourage users to always use the mechanism. If
for any reason there is a compelling reason not to use chroot (e.g. access to
a server via a UNIX socket with an unconvenient path), it remains possible to
silence the warning by adding an explicit "chroot /", which has the benefit
of being visible in a configuration.

Define a time window during which idle connections and active connections
closing is spread in case of soft-stop. After a SIGUSR1 is received and the
grace period is over (if any), the idle connections will all be closed at
once if this option is not set, and active HTTP or HTTP2 connections will be
ended after the next request is received, either by appending a "Connection:
close" line to the HTTP response, or by sending a GOAWAY frame in case of
HTTP2. When this option is set, connection closing will be spread over this
set <time>.
If the close-spread-time is set to "infinite", active connection closing
during a soft-stop will be disabled. The "Connection: close" header will not
be added to HTTP responses (or GOAWAY for HTTP2) anymore and idle connections
will only be closed once their timeout is reached (based on the various
timeouts set in the configuration).

<time>  is a time window (by default in milliseconds) during which
        connection closing will be spread during a soft-stop operation, or
        "infinite" if active connection closing should be disabled.

It is recommended to set this setting to a value lower than the one used in
the "hard-stop-after" option if this one is used, so that all connections
have a chance to gracefully close before the process stops.

Define an ASCII string secret shared between several nodes belonging to the
same cluster. It could be used for different usages. It is at least used to
derive stateless reset tokens for all the QUIC connections instantiated by
this process. This is also the case to derive secrets used to encrypt Retry
tokens.

If this parameter is not set, a random value will be selected on process
startup. This allows to use features which rely on it, albeit with some
limitations.

On some operating systems, it is possible to bind a thread group or a thread
to a specific CPU set. This means that the designated threads will never run
on other CPUs. The "cpu-map" directive specifies CPU sets for individual
threads or thread groups. The first argument is a thread group range,
optionally followed by a thread set. These ranges have the following format:

    all | odd | even | number[-[number]]

<number> must be a number between 1 and 32 or 64, depending on the machine's
word size. Any group IDs above 'thread-groups' and any thread IDs above the
machine's word size are ignored. All thread numbers are relative to the group
they belong to. It is possible to specify a range with two such number
delimited by a dash ('-'). It also is possible to specify all threads at once
using "all", only odd numbers using "odd" or even numbers using "even", just
like with the "thread
This keyword is available in sections :
Bind options
Fetching samples from internal states" bind directive. The second and forthcoming arguments
are CPU sets. Each CPU set is either a unique number starting at 0 for the
first CPU or a range with two such numbers delimited by a dash ('-'). These
CPU numbers and ranges may be repeated by delimiting them with commas or by
passing more ranges as new arguments on the same line. Outside of Linux and
BSD operating systems, there may be a limitation on the maximum CPU index to
either 31 or 63. Multiple "cpu-map" directives may be specified, but each
"cpu-map" directive will replace the previous ones when they overlap.

Ranges can be partially defined. The higher bound can be omitted. In such
case, it is replaced by the corresponding maximum value, 32 or 64 depending
on the machine's word size.

The prefix "auto:" can be added before the thread set to let HAProxy
automatically bind a set of threads to a CPU by incrementing threads and
CPU sets. To be valid, both sets must have the same size. No matter the
declaration order of the CPU sets, it will be bound from the lowest to the
highest bound. Having both a group and a thread range with the "auto:"
prefix is not supported. Only one range is supported, the other one must be
a fixed number.

Note that group ranges are supported for historical reasons. Nowadays, a lone
number designates a thread group and must be 1 if thread-groups are not used,
and specifying a thread range or number requires to prepend "1/" in front of
it if thread groups are not used. Finally, "1" is strictly equivalent to
"1/all" and designates all threads in the group.

cpu-map 1/all 0-3 # bind all threads of the first group on the
                  # first 4 CPUs

cpu-map 1/1- 0-   # will be replaced by "cpu-map 1/1-64 0-63"
                  # or "cpu-map 1/1-32 0-31" depending on the machine's
                  # word size.

# all these lines bind thread 1 to the cpu 0, the thread 2 to cpu 1
# and so on.
cpu-map auto:1/1-4   0-3
cpu-map auto:1/1-4   0-1 2-3
cpu-map auto:1/1-4   3 2 1 0
cpu-map auto:1/1-4   3,2,1,0

# bind each thread to exactly one CPU using all/odd/even keyword
cpu-map auto:1/all   0-63
cpu-map auto:1/even  0-31
cpu-map auto:1/odd   32-63

# invalid cpu-map because thread and CPU sets have different sizes.
cpu-map auto:1/1-4   0    # invalid
cpu-map auto:1/1     0-3  # invalid

# map 40 threads of those 4 groups to individual CPUs
cpu-map auto:1/1-10   0-9
cpu-map auto:2/1-10   10-19
cpu-map auto:3/1-10   20-29
cpu-map auto:4/1-10   30-39

# Map 80 threads to one physical socket and 80 others to another socket
# without forcing assignment. These are split into 4 groups since no
# group may have more than 64 threads.
cpu-map 1/1-40   0-39,80-119    # node0, siblings 0 & 1
cpu-map 2/1-40   0-39,80-119
cpu-map 3/1-40   40-79,120-159  # node1, siblings 0 & 1
cpu-map 4/1-40   40-79,120-159

Defines how you want threads to be bound to cpus.
It currently accepts the following values :
- per-core: each thread will be bound to all the hardware threads of one core.
- per-group: each thread will be bound to all the hardware threads of the
  group. This is the default unless "threads-per-core 1" is used in
  "cpu-policy". "per-group" accepts an optional argument, to specify how CPUs
  should be allocated. When a list of CPUs is larger than the maximum allowed
  number of CPUs per group and has to be split between multiple groups, an
  extra option allows to choose how the groups will be bound to those CPUs:
  - auto: each thread group will only be assigned a fair share of contiguous
    CPU cores that are dedicated to it and not shared with other groups. This
    is the default as it generally is more optimal.
  - loose: each group will still be allowed to use any CPU in the list. This
    generally causes more contention, but may sometimes help deal better with
    parasitic loads running on the same CPUs.
- auto: "per-group" will be used, unless "threads-per-core 1" is used in
  "cpu-policy", in which case "per-core" will be used. This is the default.
- per-thread: that will bind one thread to one hardware thread only. If
  "threads-per-core 1" is used in "cpu-policy", then each thread will be
  bound to one hardware thread of a different core.
- per-ccx: each thread will be bound to all the hardware threads of a CCX.

Selects the CPU allocation policy to be used.

On multi-CPU systems, there can be plenty of reasons for not using all
available CPU cores, and/or for grouping them into different thread groups,
for performance, latency, cost, or system-wide resource management. The
"cpu-set" directive already allows to evict a number of them, but once done,
it is necessary to decide how to assign the remaining ones to threads and
thread groups.

This mapping is normally performed using the "cpu-map" directive, though it
can be particularly difficult to maintain on heterogeneous systems.

The "cpu-policy" directive chooses between a small number of allocation
policies which one to use instead, when "cpu-map" is not used. The following
policies are currently supported, with "performance" being the default one:

 - none               no particular post-selection is performed. All enabled
                      CPUs will be usable, and if the number of threads is
                      not set, it will be set to the number of available CPUs
                      but no more than 32 for 32-bit systems or 64 for 64-bit
                      systems, per thread-group. The number of thread-groups,
                      if not set, will be set to 1.

 - efficiency         exactly like "group-by-ccx" below, except that CPU
                      clusters composed of cores whose performance is more
                      than 25% above that of the next less performant one are
                      evicted. These are typically "big" or "performance"
                      cores. This means that if more than one type of CPU
                      cores are detected, only the efficient one will be
                      used. This can make sense for use with moderate loads
                      when the most powerful cores need to be available to
                      the application or a security component. Some modern
                      CPUs have a large number of such efficient CPU cores
                      which can collectively deliver a decent level of
                      performance while using less power.

 - first-usable-node  if the CPUs were not previously restricted at boot (for
                      example using the "taskset" utility), and if the
                      "nbthread" directive was not set, then the first NUMA
                      node with enabled CPUs will be used, and this number of
                      CPUs will be used as the number of threads. A single
                      thread group will be enabled with all of them, within
                      the limit of 32 or 64 depending on the system.

 - group-by-2-ccx     same as "group-by-ccx" below but create a group every
                      two CCX. This can make sense on CPUs having many CCX of
                      few cores each, to avoid creating many groups, or to
                      smooth the distribution a little bit when not all cores
                      are in use. Please note that it can have very bad
                      performance effects when the communication between CCX
                      is slow. This is generally recommended against.

 - group-by-2-clusters same as "group-by-cluster" but create a group every
                      two clusters. This can make sense on CPUs having many
                      clusters of few cores each, to avoid creating many
                      groups, or to smooth the distribution a little bit when
                      not all cores are in use. Please note that it can have
                      very bad performance effects when the communication
                      between clusters is slow. This is generally recommended
                      against.

 - group-by-3-ccx     same as "group-by-ccx" below but create a group every
                      three CCX. This can make sense on CPUs having many CCX
                      of few cores each, to avoid creating many groups, or to
                      smooth the distribution a little bit when not all cores
                      are in use. Please note that it can have very bad
                      performance effects when the communication between CCX
                      is slow. This is generally recommended against.

 - group-by-3-clusters same as "group-by-cluster" but create a group every
                      three clusters. This can make sense on CPUs having many
                      clusters of few cores each, to avoid creating many
                      groups, or to smooth the distribution a little bit when
                      not all cores are in use. Please note that it can have
                      very bad performance effects when the communication
                      between clusters is slow. This is generally recommended
                      against.

 - group-by-4-ccx     same as "group-by-ccx" below but create a group every
                      four CCX. This can make sense on CPUs having many CCX
                      of few cores each, to avoid creating many groups, or to
                      smooth the distribution a little bit when not all cores
                      are in use. Please note that it can have very bad
                      performance effects when the communication between CCX
                      is slow. This is generally recommended against.

 - group-by-4-clusters same as "group-by-cluster" but create a group every
                      four clusters. This can make sense on CPUs having many
                      clusters of few cores each, to avoid creating many
                      groups, or to smooth the distribution a little bit when
                      not all cores are in use. Please note that it can have
                      very bad performance effects when the communication
                      between clusters is slow. This is generally recommended
                      against.

 - group-by-ccx       if neither "nbthread" not "nbtgroups" were set, then
                      one thread group is created for each CPU core complex
                      ("CCX") with available CPUs, each with as many threads
                      as CPUs. A CCX groups CPUs having a similarly fast
                      access to the last level cache ("LLC"), typically the
                      L3 cache. On most modern machines, it is critical for
                      performance not to mix CPUs from distant CCX in the
                      same thread group. All threads of a group are then
                      bound to all CPUs of the CCX so that intra-group
                      communications remain local to the CCX without
                      enforcing too strong a binding. The per-group thread
                      limits and thread-group limits are respected. This is
                      recommended on multi-socket and NUMA systems, as well
                      as CPUs with bad inter-CCX latencies.

 - group-by-cluster   if neither "nbthread" not "nbtgroups" were set, then
                      one thread group is created for each CPU cluster with
                      available CPUs, each with as many threads as CPUs. All
                      threads of a group are bound to all CPUs of the cluster
                      so that intra-group communications remain local to the
                      cluster without enforcing too strong a binding. The
                      per-group thread limits and thread-group limits are
                      respected. This is recommended on multi-socket and NUMA
                      systems, as well as CPUs with bad inter-CCX latencies.
                      On most server machines, clusters and CCX are the same,
                      but on heterogeneous machines ("performance" vs
                      "efficiency" or "big" vs "little"), a cluster will
                      generally be made of only a part of a CCX composed only
                      of very similar CPUs (same type, +/-5% frequency
                      difference max). The difference is visible on modern
                      laptops and desktop machines used by developers and
                      admins to validate setups.

 - performance        exactly like "group-by-ccx" above, except that CPU
                      clusters composed of cores whose performance is less
                      than 80% of those of the next more performant one are
                      evicted. These are typically "little" or "efficient"
                      cores, whose addition generally doesn't bring significant
                      gains and can easily be counter-productive (e.g. TLS
                      handshakes). Often, keeping such cores for other tasks
                      such as network handling is much more effective. On
                      development systems, these can also be used to run
                      auxiliary tools such as load generators and monitoring
                      tools. This is the default policy.

 - resource           this is like "group-by-cluster" above, except that only
                      the smallest and most efficient CPU cluster will be
                      used, while all other ones will be ignored. This can be
                      used to limit the resource usage to the strict minimum
                      that still delivers decent performance, for example to
                      try to further reduce power consumption or minimize the
                      number of cores needed on some rented systems for a
                      sidecar setup, in order to scale the system down more
                      easily. Note that if a single cluster is present, it
                      will still be fully used.

An optional keyword can be added, "threads-per-core". It can accept two
values, "1" and "auto". If set to 1, then only one thread per core will be
created, unrespective of how many hardware threads the core has. If set
to auto, then one thread per hardware thread will be created.
If no affinity is specified, and threads-per-core 1 is used, then by
default the affinity will be per-core.

Allows to symbolically describe what sets of CPUs to run on. The directive
supports the following keyword:
  - reset              this undoes any previous limitation that could have
                       been inherited by a service manager or a "taskset"
                       command for example.
  - drop-cpu <set>     do not bind to CPUs in this set
  - only-cpu <set>     do not bind to CPUs not in this set
  - drop-node <set>    do not bind to CPUs belonging to this NUMA node
  - only-node <set>    do not bind to CPUs not belonging to this NUMA node
  - drop-cluster <set> do not bind to CPUs on this hardware cluster number
  - only-cluster <set> do not bind to CPUs on other hardware cluster number
  - drop-core <set>    do not bind to CPUs on this hardware core number
  - only-core <set>    do not bind to CPUs on other hardware core number
  - drop-thread <set>  do not bind to CPUs on this hardware thread number
  - only-thread <set>  do not bind to CPUs on other hardware thread number

Assigns a default directory to fetch SSL certificates from when a relative
path is used with "crtfile" or "crt
This keyword is available in sections :
Load options
Bind options
Server and default-server options" directives. Absolute locations specified
prevail and ignore "crt-base
This keyword is available in sections :
Certificate Storage
Process management and security".

Makes the process fork into background. This is the recommended mode of
operation. It is equivalent to the command line "-D" argument. It can be
disabled by the command line "-db" argument. This option is ignored in
systemd mode.

By default HAProxy loads all files designated by a relative path from the
location the process is started in. In some circumstances it might be
desirable to force all relative paths to start from a different location
just as if the process was started from such locations. This is what this
directive is made for. Technically it will perform a temporary chdir() to
the designated location while processing each configuration file, and will
return to the original directory after processing each file. It takes an
argument indicating the policy to use when loading files whose path does
not start with a slash ('/'):
  - "current" indicates that all relative files are to be loaded from the
    directory the process is started in ; this is the default.

  - "config" indicates that all relative files should be loaded from the
    directory containing the configuration file. More specifically, if the
    configuration file contains a slash ('/'), the longest part up to the
    last slash is used as the directory to change to, otherwise the current
    directory is used. This mode is convenient to bundle maps, errorfiles,
    certificates and Lua scripts together as relocatable packages. When
    multiple configuration files are loaded, the directory is updated for
    each of them.

  - "parent" indicates that all relative files should be loaded from the
    parent of the directory containing the configuration file. More
    specifically, if the configuration file contains a slash ('/'), ".."
    is appended to the longest part up to the last slash is used as the
    directory to change to, otherwise the directory is "..". This mode is
    convenient to bundle maps, errorfiles,  certificates and Lua scripts
    together as relocatable packages, but where each part is located in a
    different subdirectory (e.g. "config/", "certs/", "maps/", ...).

  - "origin" indicates that all relative files should be loaded from the
    designated (mandatory) path. This may be used to ease management of
    different HAProxy instances running in parallel on a system, where each
    instance uses a different prefix but where the rest of the sections are
    made easily relocatable.

Each "default-path" directive instantly replaces any previous one and will
possibly result in switching to a different directory. While this should
always result in the desired behavior, it is really not a good practice to
use multiple default-path directives, and if used, the policy ought to remain
consistent across all configuration files.

Warning: some configuration elements such as maps or certificates are
uniquely identified by their configured path. By using a relocatable layout,
it becomes possible for several of them to end up with the same unique name,
making it difficult to update them at run time, especially when multiple
configuration files are loaded from different directories. It is essential to
observe a strict collision-free file naming scheme before adopting relative
paths. A robust approach could consist in prefixing all files names with
their respective site name, or in doing so at the directory level.

Add a text that describes the instance.

Please note that it is required to escape certain characters (# for example)
and this text is inserted into a html page so you should avoid using
"<" and ">" characters.

Sets the path of the DeviceAtlas JSON data file to be loaded by the API.
The path must be a valid JSON data file and accessible by HAProxy process.

Sets the level of information returned by the API. This directive is
optional and set to 0 by default if not set.

Sets the client cookie's name used for the detection if the DeviceAtlas
Client-side component was used during the request. This directive is optional
and set to DAPROPS by default if not set.

Sets the character separator for the API properties results. This directive
is optional and set to | by default if not set.

By default, DNS resolvers accept both IPv4 and IPv6 addresses. This can be
influenced by the "resolve-prefer" keywords on server lines as well as the
family argument to the "do-resolve" action, but that is only a preference,
which does not block the other family from being used when it's alone. In
some environments where dual-stack is not usable, stumbling on an unreachable
IPv6-only DNS record can cause significant trouble as it will replace a
previous IPv4 one which would possibly have continued to work till next
request. The "dns-accept-family" global option permits to enforce usage of
only one (or both) address families. The argument is a comma-delimited list
of the following words:
  - "ipv4": query and accept IPv4 addresses ("A" records)
  - "ipv6": query and accept IPv6 addresses ("AAAA" records)
  - "auto": use IPv4, and IPv6 if the system has a default gateway for it.
            The result of the last check is cached for 30 seconds.

When a single family is used, no request will be sent to resolvers for the
other family, and any response for the other family will be ignored. The
default value since 3.3 is "auto", which effectively enables both families
only once IPv6 has been proven to be routable, otherwise sticks to IPv4.

This statement must appear before using some directives tagged as deprecated
to silent warnings and make sure the config file will not be rejected. Not
all deprecated directives are concerned, only those without any alternative
solution.

This statement must appear before using directives tagged as experimental or
the config file will be rejected. Please note that features covered by this
option are not guaranteed to work well and may break during the maintenance
cycle. Developers will maintain them in best effort mode while the next
version is being worked on, and will deploy any reasonable effort to avoid
breaking them but with no guarantee. For these reasons, these features are
not expected to be supported beyond the release of the next LTS release.
Users who want to try experimental features are expected to upgrade quickly
to benefit from the improvements made to that feature. In order to know if
this directive is still needed, it's easy: if it is enabled without being
used by any such feature, a warning will be emitted suggesting to turn it
off. So without any warning, it means it's still needed.

Allows the use of an external agent to perform health checks. This is
disabled by default as a security precaution, and even when enabled, checks
may still fail unless "insecure-fork-wanted" is enabled as well. If the
program launched makes use of a setuid executable (it should really not),
you may also need to set "insecure-setuid-wanted" in the global section.
By default, the checks start with a clean environment which only contains
variables defined in the "external-check
This keyword is available in sections :
Process management and security
Alphabetically sorted keywords reference" command in the backend section. It
may sometimes be desirable to preserve the environment though, for example
when complex scripts retrieve their extra paths or information there. This
can be done by appending the "preserve-env" keyword. In this case however it
is strongly advised not to run a setuid nor as a privileged user, as this
exposes the check program to potential attacks. See "option external-check",
and "insecure-fork-wanted", and "insecure-setuid-wanted" for extra details.

Sets an upper bound to the maximum number of file descriptors that the
process will use, regardless of system limits. While "ulimit-n" and "maxconn
This keyword is available in sections :
Log forwarding
Performance tuning
Alphabetically sorted keywords reference
Bind options
Server and default-server options"
may be used to enforce a value, when they are not set, the process will be
limited to the hard limit of the RLIMIT_NOFILE setting as reported by
"ulimit -n -H". But some modern operating systems are now allowing extremely
large values here (in the order of 1 billion), which will consume way too
much RAM for regular usage. The fd-hard-limit setting is provided to enforce
a possibly lower bound to this limit. This means that it will always respect
the system-imposed limits when they are below <number> but the specified
value will be used if system-imposed limits are higher. By default
fd-hard-limit is set to 1048576. This default could be changed via
DEFAULT_MAXFD compile-time variable, that could serve as the maximum (kernel)
system limit, if RLIMIT_NOFILE hard limit is extremely large. fd-hard-limit
set in global section allows to temporarily override the value provided via
DEFAULT_MAXFD at the build-time. In the example below, no other setting is
specified and the maxconn value will automatically adapt to the lower of
"fd-hard-limit" and the RLIMIT_NOFILE limit:

    global
        # use as many FDs as possible but no more than 50000
        fd-hard-limit 50000

Changes the process's group ID to <number>. It is recommended that the group
ID is dedicated to HAProxy or to a small set of similar daemons. HAProxy must
be started with a user belonging to this group, or with superuser privileges.
Note that if HAProxy is started from a user having supplementary groups, it
will only be able to drop these groups if started with superuser privileges.
See also "group
This keyword is available in sections :
Userlists
Process management and security
Bind options" and "uid
This keyword is available in sections :
Process management and security
Bind options".

Defines a delay between SIGUSR1 and real soft-stop.

<time>  is an extra delay (by default in milliseconds) after receipt of the
        SIGUSR1 signal that will be waited for before proceeding with the
        soft-stop operation.

This is used for compatibility with legacy environments where the haproxy
process needs to be stopped but some external components need to detect the
status before listeners are unbound. The principle is that the internal
"stopping" variable (which is reported by the "stopping" sample fetch
function) will be turned to true, but listeners will continue to accept
connections undisturbed, until the delay expires, after what the regular
soft-stop will proceed. This must not be used with processes that are
reloaded, or this will prevent the old process from unbinding, and may
prevent the new one from starting, or simply cause trouble.

global
  grace 10s

# Returns 200 OK until stopping is set via SIGUSR1
frontend ext-check
  bind :9999
  monitor-uri /ext-check
  monitor fail if { stopping }

Please note that a more flexible and durable approach would instead consist
for an orchestration system in setting a global variable from the CLI, use
that variable to respond to external checks, then after a delay send the
SIGUSR1 signal.

# Returns 200 OK until proc.stopping is set to non-zero. May be done
# from HTTP using set-var(proc.stopping) or from the CLI using:
# > set var proc.stopping int(1)
frontend ext-check
  bind :9999
  monitor-uri /ext-check
  monitor fail if { var(proc.stopping) -m int gt 0 }

Similar to "gid
This keyword is available in sections :
Process management and security
Bind options" but uses the GID of group name <group name> from /etc/group.
See also "gid
This keyword is available in sections :
Process management and security
Bind options" and "user
This keyword is available in sections :
Userlists
Process management and security
Bind options".

Does not reject HTTP/1.0 GET/HEAD/DELETE requests with a payload with a
413 Payload Too Large HTTP response.

While It is explicitly allowed in HTTP/1.1, HTTP/1.0 is not clear on this
point and some old servers don't expect any payload and never look for body
length (via Content-Length or Transfer-Encoding headers). It means that some
intermediaries may properly handle the payload for HTTP/1.0 GET/HEAD/DELETE
requests, while some others may totally ignore it. That may lead to security
issues because a request smuggling attack is possible. Thus, by default,
HAProxy rejects HTTP/1.0 GET/HEAD/DELETE requests with a payload.

However, it may be an issue with some old clients. In this case, this global
option may be set.

As mandated by the HTTP/1.1 specification (RFC9112#6.1), the presence of both
a Transfer-Encoding header field and a Content-Length header field in the
same message represents a serious risk of conveying a content smuggling
attack if there are any HTTP/1.0 agent anywhere in the upstream of downstream
chain, and when facing this, an agent must absolutely close the connection
after the response so as to prevent any exploitation. But this may have a
performance impact on some very old clients, especially if they need to
renegotiate a TLS connection for every request. This option is present to
ask HAProxy not to enforce this rule, and to just sanitize the message but
leave the connection alive after the response. This may only be done when
absolutely certain that no HTTP/1.0 agents are present in the chain and that
all implementations before HAProxy are fully HTTP/1.1 compliant regarding the
rules that apply to these header fields. In any case, HAProxy will continue
to ignore and drop the extraneous Content-Length header so as not to confuse
the next hop.

When enabling this option to work around an old broken client or server, it
is important to understand that regardless of the need or not for this
option, such an agent violating this rule faces a risk to see its messages
truncated by old agents that would consider Content-Length and ignore
Transfer-Encoding, since the cumulated size of the encoded chunk sizes are
not being accounted for. As such, the rule above is not just a matter of
security but also of taking care of getting rid of agents that may face
communication trouble due to incompatibilities with older ones.

Defines the case adjustment to apply, when enabled, to the header name
<from>, to change it to <to> before sending it to HTTP/1 clients or
servers. <from> must be in lower case, and <from> and <to> must not differ
except for their case. It may be repeated if several header names need to be
adjusted. Duplicate entries are not allowed. If a lot of header names have to
be adjusted, it might be more convenient to use "h1-case-adjust-file".
Please note that no transformation will be applied unless "option
h1-case-adjust-bogus-client" or "option h1-case-adjust-bogus-server" is
specified in a proxy.

There is no standard case for header names because, as stated in RFC7230,
they are case-insensitive. So applications must handle them in a case-
insensitive manner. But some bogus applications violate the standards and
erroneously rely on the cases most commonly used by browsers. This problem
becomes critical with HTTP/2 because all header names must be exchanged in
lower case, and HAProxy follows the same convention. All header names are
sent in lower case to clients and servers, regardless of the HTTP version.

Applications which fail to properly process requests or responses may require
to temporarily use such workarounds to adjust header names sent to them for
the time it takes the application to be fixed. Please note that an
application which requires such workarounds might be vulnerable to content
smuggling attacks and must absolutely be fixed.

global
  h1-case-adjust content-length Content-Length

See "h1-case-adjust-file", "option h1-case-adjust-bogus-client" and
"option h1-case-adjust-bogus-server".

Defines a file containing a list of key/value pairs used to adjust the case
of some header names before sending them to HTTP/1 clients or servers. The
file <hdrs-file> must contain 2 header names per line. The first one must be
in lower case and both must not differ except for their case. Lines which
start with '#' are ignored, just like empty lines. Leading and trailing tabs
and spaces are stripped. Duplicate entries are not allowed. Please note that
no transformation will be applied unless "option h1-case-adjust-bogus-client"
or "option h1-case-adjust-bogus-server" is specified in a proxy.

If this directive is repeated, only the last one will be processed.  It is an
alternative to the directive "h1-case-adjust" if a lot of header names need
to be adjusted. Please read the risks associated with using this.

See "h1-case-adjust", "option h1-case-adjust-bogus-client" and
"option h1-case-adjust-bogus-server".

This disables the announcement of the support for h2 websockets to clients.
This can be use to overcome clients which have issues when implementing the
relatively fresh RFC8441, such as Firefox 88. To allow clients to
automatically downgrade to http/1.1 for the websocket tunnel, specify h2
support on the bind line using "alpn
This keyword is available in sections :
Bind options
Server and default-server options" without an explicit "proto
This keyword is available in sections :
Bind options
Server and default-server options" keyword. If
this statement was previously activated, this can be disabled by prefixing
the keyword with "no".

Defines the maximum time allowed to perform a clean soft-stop.

<time>  is the maximum time (by default in milliseconds) for which the
        instance will remain alive when a soft-stop is received via the
        SIGUSR1 signal.

This may be used to ensure that the instance will quit even if connections
remain opened during a soft-stop (for example with long timeouts for a proxy
in tcp mode). It applies both in TCP and HTTP mode.

global
  hard-stop-after 30s

Toggle per protocol protection which forbid communication with clients which
use privileged ports as their source port. This range of ports is defined
according to RFC 6335. By default, protection is active for QUIC protocol as
this behavior is suspicious and may be used as a spoofing or DNS/NTP
amplification attack.

Replace, reduce or extend the list of status codes that define an error as
considered by the termination codes and the "http_err_cnt" counter in stick
tables. The default range for errors is 400 to 499, but in certain contexts
some users prefer to exclude specific codes, especially when tracking client
errors (e.g. 404 on systems with dynamically generated contents). See also
"http-fail-codes" and "http_err_cnt".

A range specified without '+' nor '-' redefines the existing range to the new
one. A range starting with '+' extends the existing range to also include the
specified one, which may or may not overlap with the existing one. A range
starting with '-' removes the specified range from the existing one. A range
consists in a number from 100 to 599, optionally followed by "-" followed by
another number greater than or equal to the first one to indicate the high
boundary of the range. Multiple ranges may be delimited by commas for a same
add/del/ replace operation.

http-err-codes 400,402-444,446-480,490   # sets exactly these codes
http-err-codes 400-499 -450 +500         # sets 400 to 500 except 450
http-err-codes -450-459                  # removes 450 to 459 from range
http-err-codes +501,505                  # adds 501 and 505 to range

Replace, reduce or extend the list of status codes that define a failure as
considered by the termination codes and the "http_fail_cnt" counter in stick
tables. The default range for failures is 500 to 599 except 501 and 505 which
can be triggered by clients, and normally indicate a failure from the server
to process the request. Some users prefer to exclude certain codes in certain
contexts where it is known they're not relevant, such as 500 in certain SOAP
environments as it doesn't translate a server fault there. The syntax is
exactly the same as for http-err-codes above. See also "http-err-codes" and
"http_fail_cnt".

By default HAProxy tries hard to prevent any thread and process creation
after it starts. Doing so is particularly important when using Lua files of
uncertain origin, and when experimenting with development versions which may
still contain bugs whose exploitability is uncertain. And generally speaking
it's good hygiene to make sure that no unexpected background activity can be
triggered by traffic. But this prevents external checks from working, and may
break some very specific Lua scripts which actively rely on the ability to
fork. This option is there to disable this protection. Note that it is a bad
idea to disable it, as a vulnerability in a library or within HAProxy itself
will be easier to exploit once disabled. In addition, forking from Lua or
anywhere else is not reliable as the forked process may randomly embed a lock
set by another thread and never manage to finish an operation. As such it is
highly recommended that this option is never used and that any workload
requiring such a fork be reconsidered and moved to a safer solution (such as
agents instead of external checks). This option supports the "no" prefix to
disable it. This can also be activated with "-dI" on the haproxy command
line.

HAProxy doesn't need to call executables at run time (except when using
external checks which are strongly recommended against), and is even expected
to isolate itself into an empty chroot. As such, there basically is no valid
reason to allow a setuid executable to be called without the user being fully
aware of the risks. In a situation where HAProxy would need to call external
checks and/or disable chroot, exploiting a vulnerability in a library or in
HAProxy itself could lead to the execution of an external program. On Linux
it is possible to lock the process so that any setuid bit present on such an
executable is ignored. This significantly reduces the risk of privilege
escalation in such a situation. This is what HAProxy does by default. In case
this causes a problem to an external check (for example one which would need
the "ping" command), then it is possible to disable this protection by
explicitly adding this directive in the global section. If enabled, it is
possible to turn it back off by prefixing it with the "no" keyword.

Assigns a directory to load certificate chain for issuer completion. All
files must be in PEM format. For certificates loaded with "crt
This keyword is available in sections :
Load options
Bind options
Server and default-server options" or "crt-list",
if certificate chain is not included in PEM (also commonly known as
intermediate certificate), HAProxy will complete chain if the issuer of the
certificate corresponds to the first certificate of the chain loaded with
"issuers-chain-path".
A "crt
This keyword is available in sections :
Load options
Bind options
Server and default-server options" file with PrivateKey+Certificate+IntermediateCA2+IntermediateCA1
could be replaced with PrivateKey+Certificate. HAProxy will complete the
chain if a file with IntermediateCA2+IntermediateCA1 is present in
"issuers-chain-path" directory. All other certificates with the same issuer
will share the chain in memory.

The OCSP features are able to use the completed chain when no .issuer was
used, or no chain was provided in the PEM.

Set the list of algorithms allowed in the jwt_decrypt_XXX converters. JWT
tokens using an unsupported or disabled algorithms will never be decrypted.
The specified algorithms must have the same format as in section 4.1 of
RFC7518 and must be colon-separated. The special "ALL" name can be used to
enable all the supported algorithms (see "jwt_decrypt_jwk" converter for a
complete list) and a '!' can be appended to an algorithm name to explicitly
disable it.
Please note that unless "ALL" is specified, using this option will disable
any algorithm that is not explicitly mentioned in the provided list.

# Enable all algorithms but the "ECDH-ES" one
jwt.decrypt_alg_list ALL:!ECDH-ES

# Only enable ECDH-ES algorithms
jwt.decrypt_alg_list ECDH-ES:ECDH-ES+A128KW:ECDH-ES+A192KW:ECDH-ES+A256KW

Set the list of encryption algorithms allowed in the jwt_decrypt_XXX
converters. JWT tokens using an unsupported or disabled encryption algorithms
will never be decrypted.
The specified algorithms must have the same format as in section 5.1 of
RFC7518 and must be colon-separated. The special "ALL" name can be used to
enable all the supported algorithms (see "jwt_decrypt_jwk" converter for a
complete list) and a '!' can be appended to an algorithm name to explicitly
disable it.
Please note that unless "ALL" is specified, using this option will disable
any algorithm that is not explicitly mentioned in the provided list.

# Enable only AES GCM encrypting algorithms
jwt.decrypt_enc_list A128GCM:A192GCM:A256GCM

Assigns a default directory to fetch SSL private keys from when a relative
path is used with "key" directives. Absolute locations specified prevail and
ignore "key-base
This keyword is available in sections :
Certificate Storage
Process management and security". This option only works with a crt-store load line.

This setting must be used to explicitly enable the QUIC listener bindings
when haproxy is compiled with a version of OpenSSL without QUIC support. It
activates an haproxy internal compatibility layer which must have been
selected at build time with USE_QUIC_OPENSSL_COMPAT=1. This compatibility
layer supports most of the necessary TLS operations, albeit without QUIC
0-RTT capability.

This feature is primarily targeted for OpenSSL prior to version 3.5.2, where
QUIC API was not implemented or only partially. The compatibility layer can
still be activated for version 3.5.2 and above, but this is probably
unnecessary.

If limited-quic is set but the compatibility layer was not selected at build
time, the option is silently ignored and QUIC TLS operations rely on the TLS
library.

Sets the local instance's peer name. It will be ignored if the "-L"
command line argument is specified or if used after "peers" section
definitions. In such cases, a warning message will be emitted during
the configuration parsing.

This option will also set the HAPROXY_LOCALPEER environment variable.
See also "-L" in the management guide and "peers" section below.

Adds a global syslog server. Several global servers can be defined. They
will receive logs for starts and exits, as well as all logs from proxies
configured with "log global
This keyword is available in sections :
Log forwarding
Alphabetically sorted keywords reference". See "log
This keyword is available in sections :
Peers declaration
Log forwarding
Process management and security
Alphabetically sorted keywords reference" option for proxies for more details.

Sets the hostname field in the syslog header. If optional "string" parameter
is set the header is set to the string contents, otherwise uses the hostname
of the system. Generally used if one is not relaying logs through an
intermediate syslog server or for simply customizing the hostname printed in
the logs.

Sets the tag field in the syslog header to this string. It defaults to the
program name as launched from the command line, which usually is "haproxy".
Sometimes it can be useful to differentiate between multiple processes
running on the same host. See also the per-proxy "log-tag
This keyword is available in sections :
Process management and security
Alphabetically sorted keywords reference
Log profiles" directive.

This global directive loads and executes a Lua file in the shared context
that is visible to all threads. Any variable set in such a context is visible
from any thread. This is the easiest and recommended way to load Lua programs
but it will not scale well if a lot of Lua calls are performed, as only one
thread may be running on the global state at a time. A program loaded this
way will always see 0 in the "core.thread" variable. This directive can be
used multiple times.

args are available in the lua file using the code below in the body of the
file. Do not forget that Lua arrays start at index 1. A "local" variable
declared in a file is available in the entire file and not available on
other files.

   local args = table.pack(...)

This global directive loads and executes a Lua file into each started thread.
Any global variable has a thread-local visibility so that each thread could
see a different value. As such it is strongly recommended not to use global
variables in programs loaded this way. An independent copy is loaded and
initialized for each thread, everything is done sequentially and in the
thread's numeric order from 1 to nbthread. If some operations need to be
performed only once, the program should check the "core.thread" variable to
figure what thread is being initialized. Programs loaded this way will run
concurrently on all threads and will be highly scalable. This is the
recommended way to load simple functions that register sample-fetches,
converters, actions or services once it is certain the program doesn't depend
on global variables. For the sake of simplicity, the directive is available
even if only one thread is used and even if threads are disabled (in which
case it will be equivalent to lua-load). This directive can be used multiple
times.

See lua-load for usage of args.

Prepends the given string followed by a semicolon to Lua's package.<type>
variable.
<type> must either be "path" or "cpath". If <type> is not given it defaults
to "path".

Lua's paths are semicolon delimited lists of patterns that specify how the
`require` function attempts to find the source file of a library. Question
marks (?) within a pattern will be replaced by module name. The path is
evaluated left to right. This implies that paths that are prepended later
will be checked earlier.

As an example by specifying the following path:

  lua-prepend-path /usr/share/haproxy-lua/?/init.lua
  lua-prepend-path /usr/share/haproxy-lua/?.lua

When `require "example"` is being called Lua will first attempt to load the
/usr/share/haproxy-lua/example.lua script, if that does not exist the
/usr/share/haproxy-lua/example/init.lua will be attempted and the default
paths if that does not exist either.

See https://www.lua.org/pil/8.1.html for the details within the Lua
documentation.

Master-worker mode. It is equivalent to the command line "-W" argument.

This keyword is deprecated, please start in master-worker mode using "-W" or
"-Ws".

This mode will launch a "master" which will fork a "worker" after reading the
configuration to process the traffic. The master is used as a process manager
which will monitor the "workers".

Using this mode, you can reload HAProxy directly by sending a SIGUSR2 signal
to the master. Reloading will ask the master to read the configuration again
and fork a new worker. The previous worker will be kept until the end of its
jobs.

The master-worker mode is compatible either with the foreground or daemon
mode.

By default, if a worker exits with a bad return code, in the case of a
segfault for example, all workers will be killed, and the master will leave.
It is convenient to combine this behavior with Restart=on-failure in a
systemd unit file in order to relaunch the whole process. If you don't want
this behavior, you must use the keyword "no-exit-on-failure".

See also "-W" in the management guide.

In master-worker mode, by default, if a worker exits with a bad return code,
in the case of a segfault for example, all workers will be killed, and the
master will leave. It is convenient to combine this behavior with
Restart=on-failure in a systemd unit file in order to relaunch the whole
process.

This keyword allows to keep the remaining processes alive when a worker
crashed instead of killing everything. This need to be used with caution as
it is only meant for debugging and could put the master process in an
abnormal state.

Defines the maximum number of threads in a thread group. Unless the number
of thread groups is fixed with the "thread-groups" directive, haproxy will
create as many thread groups as needed to satisfy the requested number of
threads. The minimum value is 1, and the maximum value is 64 (on 64-bit
systems, or 32 on 32-bit systems). Lower values reduce contention caused by
atomic operations on shared states, but can increase the number of sockets
needed to create all listeners and to hold idle backend connections. Higher
values will reduce these costs, at the expense of higher CPU usage under
contented situations, and lower connection rates. The default value is 16,
which provides the best tradeoff that was experimentally found on various
tested systems, including x86_64 processors from multiple vendors, and large
Arm64 systems, both on bare metal and hypervisors.

In master-worker mode, this option limits the number of time a worker can
survive to a reload. If the worker did not leave after a reload, once its
number of reloads is greater than this number, the worker will receive a
SIGTERM. This option helps to keep under control the number of workers.
See also "show proc" in the Management Guide.

By default this value is set to 50.

This setting is only available when support for threads was built in. It
makes HAProxy run on <number> threads. "nbthread" also works when HAProxy is
started in foreground. On some platforms supporting CPU affinity, the default
"nbthread" value is automatically set to the number of CPUs the process is
bound to upon startup. This means that the thread count can easily be
adjusted from the calling process using commands like "taskset" or "cpuset".
Otherwise, this value defaults to 1. The default value is reported in the
output of "haproxy -vv". Note that values set here or automatically detected
are subject to the limit set by "thread-hard-limit" (if set).

When running on a NUMA-aware platform, this enables the "cpu-policy"
directive to inspect the topology and figure the best set of CPUs to use and
the corresponding number of threads. However, if the applied binding is non
optimal on a particular architecture, it can be disabled with the statement
'no numa-cpu-mapping'. This automatic binding is also not applied if a
'nbthread' statement is present in the configuration, if the affinity of the
process is already specified, for example via the 'cpu-map' directive or the
taskset utility, or if the cpu-policy is set to any other value. See also
"cpu-map", "cpu-policy", "cpu-set".

Disable completely the ocsp-update in HAProxy. Any ocsp-update configuration
will be ignored. Default is "off".
See option "ocsp-update" for more information about the auto update
mechanism.

Allow to use an HTTP proxy for the OCSP updates. This only works with HTTP,
HTTPS is not supported. This option will allow the OCSP updater to send
absolute URI in the request to the proxy.

Sets the maximum interval between two automatic updates of the same OCSP
response. This time is expressed in seconds and defaults to 3600 (1 hour). It
must be set to a higher value than "ocsp-update.mindelay". See
option "ocsp-update" for more information about the auto update mechanism.

Sets the minimum interval between two automatic updates of the same OCSP
response. This time is expressed in seconds and defaults to 300 (5 minutes).
It is particularly useful for OCSP response that do not have explicit
expiration times. It must be set to a lower value than
"ocsp-update.maxdelay". See option "ocsp-update" for more
information about the auto update mechanism.

Sets the default ocsp-update mode for all certificates used in the
configuration. This global option can be superseded by the crt-list
"ocsp-update" option. This option is set to "off" by default.
See option "ocsp-update" for more information about the auto update
mechanism.

Writes PIDs of all daemons into file <pidfile> when daemon mode or writes PID
of master process into file <pidfile> when master-worker mode. This option is
equivalent to the "-p" command line argument. The file must be accessible to
the user starting the process. See also "daemon" and "master-worker".

A bug in the PROXY protocol v2 implementation was present in HAProxy up to
version 2.1, causing it to emit a PROXY command instead of a LOCAL command
for health checks. This is particularly minor but confuses some servers'
logs. Sadly, the bug was discovered very late and revealed that some servers
which possibly only tested their PROXY protocol implementation against
HAProxy fail to properly handle the LOCAL command, and permanently remain in
the "down" state when HAProxy checks them. When this happens, it is possible
to enable this global option to revert to the older (bogus) behavior for the
time it takes to contact the affected components' vendors and get them fixed.
This option is disabled by default and acts on all servers having the
"send-proxy-v2" statement.

Sets environment variable <name> to value <value>. If the variable exists, it
is NOT overwritten. The changes immediately take effect so that the next line
in the configuration file sees the new value. See also "setenv", "resetenv",
and "unsetenv".

Performs a one-time open of the maximum file descriptor which results in a
pre-allocation of the kernel's data structures. This prevents short pauses
when nbthread>1 and HAProxy opens a file descriptor which requires the kernel
to expand its data structures.

Removes all environment variables except the ones specified in argument. It
allows to use a clean controlled environment before setting new values with
setenv or unsetenv. Please note that some internal functions may make use of
some environment variables, such as time manipulation functions, but also
OpenSSL or even external checks. This must be used with extreme care and only
after complete validation. The changes immediately take effect so that the
next line in the configuration file sees the new environment. See also
"setenv", "presetenv", and "unsetenv".

Specifies the directory prefix to be prepended in front of all servers state
file names which do not start with a '/'. See also "server-state-file",
"load-server-state-from-file" and "server-state-file-name".

Specifies the path to the file containing state of servers. If the path starts
with a slash ('/'), it is considered absolute, otherwise it is considered
relative to the directory specified using "server-state-base" (if set) or to
the current directory. Before reloading HAProxy, it is possible to save the
servers' current state using the stats command "show servers state". The
output of this command must be written in the file pointed by <file>. When
starting up, before handling traffic, HAProxy will read, load and apply state
for each server found in the file and available in its current running
configuration. See also "server-state-base" and "show servers state",
"load-server-state-from-file" and "server-state-file-name"

This option helps choose the core dump behavior in case of process crash.
Available options are:

- on      this enables core dumping at the process level if it was
          previously disabled.

- off     this disables a previously enabled core dumping.

- libs    this enables core dumping with an embedded copy of the binaries and
          libraries that are required for debugging. This may be requested by
          developers. In this case haproxy will try to load the libraries it
          depends on into memory and keep them preciously. If the process
          crashes, they will be dumped into the core so there is no need for
          retrieving them from the file system anymore and no risk that they
          do not match the core. This takes a few megabytes to a few tens of
          megabytes of additional RAM, so it is better not to use it on small
          systems.

This option is better left disabled by default and enabled only upon a
developer's request. By default it is disabled. Without argument, it defaults
to "on". If it has been enabled, it may still be forcibly disabled by prefixing
it with the "no" keyword or by setting it to "off". It has no impact on
performance nor stability but will try hard to re-enable core dumps that were
possibly disabled by file size limitations (ulimit -f), core size limitations
(ulimit -c), or "dumpability" of a process after changing its UID/GID (such
as /proc/sys/fs/suid_dumpable on Linux). Core dumps might still be limited by
the current directory's permissions (check what directory the file is started
from), the chroot directory's permission (it may be needed to temporarily
disable the chroot directive or to move it to a dedicated writable location),
or any other system-specific constraint. For example, some Linux flavours are
notorious for replacing the default core file with a path to an executable
not even installed on the system (check /proc/sys/kernel/core_pattern). Often,
simply writing "core", "core.%p" or "/var/log/core/core.%p" addresses the
issue. When trying to enable this option waiting for a rare issue to
re-appear, it's often a good idea to first try to obtain such a dump by
issuing, for example, "kill -11" to the "haproxy" process and verify that it
leaves a core where expected when dying.

Sets the process-wide variable '<var-name>' to the result of the evaluation
of the sample expression <expr>. The variable '<var-name>' may only be a
process-wide variable (using the 'proc.' prefix). It works exactly like the
'set-var' action in TCP or HTTP rules except that the expression is evaluated
at configuration parsing time and that the variable is instantly set. The
sample fetch functions and converters permitted in the expression are only
those using internal data, typically 'int(value)' or 'str(value)'. It is
possible to reference previously allocated variables as well. These variables
will then be readable (and modifiable) from the regular rule sets.

global
    set-var proc.current_state str(primary)
    set-var proc.prio int(100)
    set-var proc.threshold int(200),sub(proc.prio)

Sets the process-wide variable '<var-name>' to the string resulting from the
evaluation of the log-format <fmt>. The variable '<var-name>' may only be a
process-wide variable (using the 'proc.' prefix). It works exactly like the
'set-var-fmt' action in TCP or HTTP rules except that the expression is
evaluated at configuration parsing time and that the variable is instantly
set. The sample fetch functions and converters permitted in the expression
are only those using internal data, typically 'int(value)' or 'str(value)'.
It is possible to reference previously allocated variables as well. These
variables will then be readable (and modifiable) from the regular rule sets.
Please see section 8.2.6 for details on the Custom log format syntax.

global
    set-var-fmt proc.current_state "primary"
    set-var-fmt proc.bootid        "%pid|%t"

Sets a list of capabilities that must be preserved when starting and running
either as a non-root user (uid > 0), or when starting with uid 0 (root) and
switching then to a non-root. By default all permissions are lost by the uid
switch, but some are often needed when trying to connect to a server from a
foreign address during transparent proxying, or when binding to a port below
1024, e.g. when using "tune.quic.fe.sock-per-conn default-on", resulting in
setups running entirely under uid 0. Setting capabilities generally is a
safer alternative, as only the required capabilities will be preserved. The
feature is OS-specific and only enabled on Linux when USE_LINUX_CAP=1 is set
at build time. The list of supported capabilities also depends on the OS and
is enumerated by the error message displayed when an invalid capability name
or an empty one is passed. Multiple capabilities may be passed, delimited by
commas. Among those commonly used, "cap_net_raw" allows to transparently bind
to a foreign address, and "cap_net_bind_service" allows to bind to a
privileged port and may be used by QUIC. If the process is started and run
under the same non-root user, needed capabilities should be set on haproxy
binary file with setcap along with this keyword. For more details about
setting capabilities on haproxy binary, please see chapter 13.1 Linux
capabilities support in the Management guide.

global
    setcap cap_net_bind_service,cap_net_admin

Sets environment variable <name> to value <value>. If the variable exists, it
is overwritten. The changes immediately take effect so that the next line in
the configuration file sees the new value. See also "presetenv", "resetenv",
and "unsetenv".

When this directive is set, it enables the use of shared memory for storing
stats counters. <name> is used as argument to shm_open() to open the shared
memory at a unique location. It also means that the directive is only
available on systems which support shm_open(). When SHM is used for stats, all
shareable counters for frontends, backends, listeners and servers will be
stored in the SHM, provided that they have a GUID set. When reloading haproxy,
new process will try to scan the SHM for objects that could be associated to
objects defined in the configuration based on GUID and type, the goal is to be
able to preserve some counters' values upon reload. On the other hand, when
haproxy is properly stopped, the SHM objects are released, which means counters
are effectively reset. It is also possible to manually remove the file before
starting a fresh process to force a reset.

See also "guid
This keyword is available in sections :
Alphabetically sorted keywords reference
Server and default-server options", "guid-prefix" and "shm-stats-file-max-objects"

This setting defines the maximum number of objects the shared memory used
for shared counters will be able to store per thread group. It is directly
related to the maximum memory size of the shm and is used to "premap" the
shm to a given size in order to avoid runtime re-mapping. It defaults to 2k,
which should suit for most setups without risking unsuitable memory usage,
but can be easily changed if needed. haproxy will complain during startup if
this value is to low to register objects that are expected to be stored in
the shared memory. It is only relevant when "shm-stats-file" was defined.

See also "thread-groups"

This setting is only available when support for OpenSSL was built in. It sets
the default string describing the list of cipher algorithms ("cipher suite")
that are negotiated during the SSL/TLS handshake up to TLSv1.2 for all
"bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference" lines which do not explicitly define theirs. The format of the string
is defined in "man 1 ciphers" from OpenSSL man pages. For background
information and recommendations see e.g.
(https://wiki.mozilla.org/Security/Server_Side_TLS) and
(https://mozilla.github.io/server-side-tls/ssl-config-generator/). For TLSv1.3
cipher configuration, please check the "ssl-default-bind-ciphersuites" keyword.
Please check the "bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference" keyword for more information.

This setting is only available when support for OpenSSL was built in and
OpenSSL 1.1.1 or later was used to build HAProxy. It sets the default string
describing the list of cipher algorithms ("cipher suite") that are negotiated
during the TLSv1.3 handshake for all "bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference" lines which do not explicitly define
theirs. The format of the string is defined in
"man 1 ciphers" from OpenSSL man pages under the section "ciphersuites
This keyword is available in sections :
Bind options
Server and default-server options". For
cipher configuration for TLSv1.2 and earlier, please check the
"ssl-default-bind-ciphers" keyword. This setting might accept TLSv1.2
ciphersuites however this is an undocumented behavior and not recommended as
it could be inconsistent or buggy.
The default TLSv1.3 ciphersuites of OpenSSL are:
"TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:TLS_AES_128_GCM_SHA256"

TLSv1.3 only supports 5 ciphersuites:

- TLS_AES_128_GCM_SHA256
- TLS_AES_256_GCM_SHA384
- TLS_CHACHA20_POLY1305_SHA256
- TLS_AES_128_CCM_SHA256
- TLS_AES_128_CCM_8_SHA256

Please check the "bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference" keyword for more information.

global
    ssl-default-bind-ciphers ECDHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-RSA-AES128-GCM-SHA256
    ssl-default-bind-ciphersuites TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:TLS_AES_128_GCM_SHA256

This setting is only available when support for OpenSSL was built in. It sets
the default string describing the list of signature algorithms related to
client authentication for all "bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference" lines which do not explicitly define
theirs. The format of the string is a colon-delimited list of signature
algorithms. Each signature algorithm can use one of two forms: TLS1.3 signature
scheme names ("rsa_pss_rsae_sha256") or the public key algorithm + digest form
("ECDSA+SHA256"). A list can contain both forms. For more information on the
format, see SSL_CTX_set1_client_sigalgs(3). A list of signature algorithms is
also available in RFC8446 section 4.2.3 and in OpenSSL in the ssl/t1_lib.c
file.  This setting is not applicable to TLSv1.1 and earlier versions of the
protocol as the signature algorithms aren't separately negotiated in these
versions. It is not recommended to change this setting unless compatibility
with a middlebox is required.

This setting is only available when support for OpenSSL was built in. It sets
the default string describing the list of elliptic curves algorithms ("curve
suite") that are negotiated during the SSL/TLS handshake with ECDHE. The format
of the string is a colon-delimited list of curve name.
Please check the "bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference" keyword for more information.

This setting is only available when support for OpenSSL was built in. It sets
default ssl-options to force on all "bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference" lines. Please check the "bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference"
keyword to see available options.

global
   ssl-default-bind-options ssl-min-ver TLSv1.0 no-tls-tickets

This setting is only available when support for OpenSSL was built in. It
sets the default string describing the list of signature algorithms that
are negotiated during the TLSv1.2 and TLSv1.3 handshake for all "bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference" lines
which do not explicitly define theirs. The format of the string is a
colon-delimited list of signature algorithms. Each signature algorithm can
use one of two forms: TLS1.3 signature scheme names ("rsa_pss_rsae_sha256")
or the public key algorithm + digest form ("ECDSA+SHA256"). A list
can contain both forms. For more information on the format,
see SSL_CTX_set1_sigalgs(3). A list of signature algorithms is also
available in RFC8446 section 4.2.3 and in OpenSSL in the ssl/t1_lib.c file.
This setting is not applicable to TLSv1.1 and earlier versions of the
protocol as the signature algorithms aren't separately negotiated in these
versions. It is not recommended to change this setting unless compatibility
with a middlebox is required.

This setting is only available when support for OpenSSL was built in. It
sets the default string describing the list of cipher algorithms that are
negotiated during the SSL/TLS handshake up to TLSv1.2 with the server,
for all "server
This keyword is available in sections :
Peers declaration
Rings
Alphabetically sorted keywords reference" lines which do not explicitly define theirs. The format of
the string is defined in "man 1 ciphers" from OpenSSL man pages. For background
information and recommendations see e.g.
(https://wiki.mozilla.org/Security/Server_Side_TLS) and
(https://mozilla.github.io/server-side-tls/ssl-config-generator/).
For TLSv1.3 cipher configuration, please check the
"ssl-default-server-ciphersuites" keyword. Please check the "server
This keyword is available in sections :
Peers declaration
Rings
Alphabetically sorted keywords reference" keyword
for more information.

This setting is only available when support for OpenSSL was built in and
OpenSSL 1.1.1 or later was used to build HAProxy. It sets the default
string describing the list of cipher algorithms that are negotiated during
the TLSv1.3 handshake with the server, for all "server
This keyword is available in sections :
Peers declaration
Rings
Alphabetically sorted keywords reference" lines which do not
explicitly define theirs. The format of the string is defined in
"man 1 ciphers" from OpenSSL man pages under the section "ciphersuites
This keyword is available in sections :
Bind options
Server and default-server options". For
cipher configuration for TLSv1.2 and earlier, please check the
"ssl-default-server-ciphers" keyword. Please check the "server
This keyword is available in sections :
Peers declaration
Rings
Alphabetically sorted keywords reference" keyword for
more information.

This setting is only available when support for OpenSSL was built in. It sets
the default string describing the list of signature algorithms related to
client authentication for all "server
This keyword is available in sections :
Peers declaration
Rings
Alphabetically sorted keywords reference" lines which do not explicitly define
theirs. The format of the string is a colon-delimited list of signature
algorithms. Each signature algorithm can use one of two forms: TLS1.3 signature
scheme names ("rsa_pss_rsae_sha256") or the public key algorithm + digest form
("ECDSA+SHA256"). A list can contain both forms. For more information on the
format, see SSL_CTX_set1_client_sigalgs(3). A list of signature algorithms is
also available in RFC8446 section 4.2.3 and in OpenSSL in the ssl/t1_lib.c
file.  This setting is not applicable to TLSv1.1 and earlier versions of the
protocol as the signature algorithms aren't separately negotiated in these
versions. It is not recommended to change this setting unless compatibility
with a middlebox is required.

This setting is only available when support for OpenSSL was built in. It sets
the default string describing the list of elliptic curves algorithms ("curve
suite") that are negotiated during the SSL/TLS handshake with ECDHE. The format
of the string is a colon-delimited list of curve name.
Please check the "server
This keyword is available in sections :
Peers declaration
Rings
Alphabetically sorted keywords reference" keyword for more information.

This setting is only available when support for OpenSSL was built in. It sets
default ssl-options to force on all "server
This keyword is available in sections :
Peers declaration
Rings
Alphabetically sorted keywords reference" lines. Please check the "server
This keyword is available in sections :
Peers declaration
Rings
Alphabetically sorted keywords reference"
keyword to see available options.

This setting is only available when support for OpenSSL was built in. It
sets the default string describing the list of signature algorithms that
are negotiated during the TLSv1.2 and TLSv1.3 handshake for all "server
This keyword is available in sections :
Peers declaration
Rings
Alphabetically sorted keywords reference" lines
which do not explicitly define theirs. The format of the string is a
colon-delimited list of signature algorithms. Each signature algorithm can
use one of two forms: TLS1.3 signature scheme names ("rsa_pss_rsae_sha256")
or the public key algorithm + digest form ("ECDSA+SHA256"). A list
can contain both forms. For more information on the format,
see SSL_CTX_set1_sigalgs(3). A list of signature algorithms is also
available in RFC8446 section 4.2.3 and in OpenSSL in the ssl/t1_lib.c file.
This setting is not applicable to TLSv1.1 and earlier versions of the
protocol as the signature algorithms aren't separately negotiated in these
versions. It is not recommended to change this setting unless compatibility
with a middlebox is required.

This setting is only available when support for OpenSSL was built in. It sets
the default DH parameters that are used during the SSL/TLS handshake when
ephemeral Diffie-Hellman (DHE) key exchange is used, for all "bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference" lines
which do not explicitly define theirs. It will be overridden by custom DH
parameters found in a bind certificate file if any. If custom DH parameters
are not specified either by using ssl-dh-param-file or by setting them
directly in the certificate file, DHE ciphers will not be used, unless
tune.ssl.default-dh-param is set. In this latter case, pre-defined DH
parameters of the specified size will be used. Custom parameters are known to
be more secure and therefore their use is recommended.
Custom DH parameters may be generated by using the OpenSSL command
"openssl dhparam <size>", where size should be at least 2048, as 1024-bit DH
parameters should not be considered secure anymore.

This settings is only available when support for OpenSSL was built in. It
allows to define a full command line that will be called when an encrypted
certificate is loaded during init. The command could be a script or any other
program. It will be provided with the encrypted private key path as first
parameter and the user-defined "args" parameters then and should dump the
passphrase that allows to decode the encrypted private key on the standard
output.
For every new encrypted private key loaded during init, HAProxy will first
try every other already known passphrase to decode the private key and will
ultimately call the passphrase command again if none works.

This setting is only available when support for OpenSSL was built in and when
OpenSSL's version is at least 3.0. It allows to define a default property
string used when fetching algorithms in providers. It behave the same way as
the openssl propquery option and it follows the same syntax (described in
https://www.openssl.org/docs/man3.0/man7/property.html). For instance, if you
have two providers loaded, the foo one and the default one, the propquery
"?provider=foo" allows to pick the algorithm implementations provided by the
foo provider by default, and to fallback on the default provider's one if it
was not found.

This setting is only available when support for OpenSSL was built in and when
OpenSSL's version is at least 3.0. It allows to load a provider during init.
If loading is successful, any capabilities provided by the loaded provider
might be used by HAProxy. Multiple 'ssl-provider' options can be specified in
a configuration file. The providers will be loaded in their order of
appearance.

Please note that loading a provider explicitly prevents OpenSSL from loading
the 'default' provider automatically. OpenSSL also allows to define the
providers that should be loaded directly in its configuration file
(openssl.cnf for instance) so it is not necessary to use this 'ssl-provider'
option to load providers. The "show ssl providers" CLI command can be used to
show all the providers that were successfully loaded.

The default search path of OpenSSL provider can be found in the output of the
"openssl version -a" command. If the provider is in another directory, you
can set the OPENSSL_MODULES environment variable, which takes the directory
where your provider can be found.

See also "ssl-propquery" and "ssl-provider-path".

This setting is only available when support for OpenSSL was built in and when
OpenSSL's version is at least 3.0. It allows to specify the search path that
is to be used by OpenSSL for looking for providers. It behaves the same way
as the OPENSSL_MODULES environment variable. It will be used for any
following 'ssl-provider' option or until a new 'ssl-provider-path' is
defined.
See also "ssl-provider".

This setting allows to configure the way HAProxy does the lookup for the
extra SSL files. By default HAProxy adds a new extension to the filename.
(ex: with "foobar.crt" load "foobar.crt.key"). With this option enabled,
HAProxy removes the extension before adding the new one (ex: with
"foobar.crt" load "foobar.key").

Your crt file must have a ".crt" extension for this option to work.

This option is not compatible with bundle extensions (.ecdsa, .rsa. .dsa)
and won't try to remove them.

This option is disabled by default. See also "ssl-load-extra-files".

This setting alters the way HAProxy will look for unspecified files during
the loading of the SSL certificates. This option applies to certificates
associated to "bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference" lines as well as "server
This keyword is available in sections :
Peers declaration
Rings
Alphabetically sorted keywords reference" lines but some of the extra
files will not have any functional impact for "server
This keyword is available in sections :
Peers declaration
Rings
Alphabetically sorted keywords reference" line certificates.

By default, HAProxy discovers automatically a lot of files not specified in
the configuration, and you may want to disable this behavior if you want to
optimize the startup time.

"none": Only load the files specified in the configuration. Don't try to load
a certificate bundle if the file does not exist. In the case of a directory,
it won't try to bundle the certificates if they have the same basename.

"all": This is the default behavior, it will try to load everything,
bundles, sctl, ocsp, issuer, key.

"bundle": When a file specified in the configuration does not exist, HAProxy
will try to load a "cert bundle". Certificate bundles are only managed on the
frontend side and will not work for backend certificates.

Starting from HAProxy 2.3, the bundles are not loaded in the same OpenSSL
certificate store, instead it will loads each certificate in a separate
store which is equivalent to declaring multiple "crt
This keyword is available in sections :
Load options
Bind options
Server and default-server options". OpenSSL 1.1.1 is
required to achieve this. Which means that bundles are now used only for
backward compatibility and are not mandatory anymore to do an hybrid RSA/ECC
bind configuration.

To associate these PEM files into a "cert bundle" that is recognized by
HAProxy, they must be named in the following way: All PEM files that are to
be bundled must have the same base name, with a suffix indicating the key
type. Currently, three suffixes are supported: rsa, dsa and ecdsa. For
example, if www.example.com has two PEM files, an RSA file and an ECDSA
file, they must be named: "example.pem.rsa" and "example.pem.ecdsa". The
first part of the filename is arbitrary; only the suffix matters. To load
this bundle into HAProxy, specify the base name only:

bind :8443 ssl crt example.pem

Note that the suffix is not given to HAProxy; this tells HAProxy to look for
a cert bundle.

HAProxy will load all PEM files in the bundle as if they were configured
separately in several "crt
This keyword is available in sections :
Load options
Bind options
Server and default-server options".

The bundle loading does not have an impact anymore on the directory loading
since files are loading separately.

On the CLI, bundles are seen as separate files, and the bundle extension is
required to commit them.

OCSP files (.ocsp), issuer files (.issuer), Certificate Transparency (.sctl)
as well as private keys (.key) are supported with multi-cert bundling.

"sctl": Try to load "<basename>.sctl" for each crt keyword. If provided for
a backend certificate, it will be loaded but will not have any functional
impact.

"ocsp": Try to load "<basename>.ocsp" for each crt keyword. If provided for
a backend certificate, it will be loaded but will not have any functional
impact.

"issuer": Try to load "<basename>.issuer" if the issuer of the OCSP file is
not provided in the PEM file. If provided for a backend certificate, it will
be loaded but will not have any functional impact.

"key": If the private key was not provided by the PEM file, try to load a
file "<basename>.key" containing a private key.

The default behavior is "all".

ssl-load-extra-files bundle sctl
ssl-load-extra-files sctl ocsp issuer
ssl-load-extra-files none

This directive allows to chose the OpenSSL security level as described in
https://www.openssl.org/docs/man1.1.1/man3/SSL_CTX_set_security_level.html
The security level will be applied to every SSL contextes in HAProxy.
Only a value between 0 and 5 is supported.

The default value depends on your OpenSSL version, distribution and how was
compiled the library.

This directive requires at least OpenSSL 1.1.1.

The default behavior for SSL verify on servers side. If specified to 'none',
servers certificates are not verified. The default is 'required' except if
forced using cmdline option '-dV'.

Self issued CA, aka x509 root CA, is the anchor for chain validation: as a
server is useless to send it, client must have it. Standard configuration
need to not include such CA in PEM file. This option allows you to keep such
CA in PEM file without sending it to the client. Use case is to provide
issuer for ocsp without the need for '.issuer' file and be able to share it
with 'issuers-chain-path'. This concerns all certificates without intermediate
certificates. It's useless for BoringSSL, .issuer is ignored because ocsp
bits does not need it. Requires at least OpenSSL 1.0.2.

Activates or deactivates the calculation of stats max counters. If you
don't need them, deactivating them may increase performances a bit.
The default is on.

By default, the stats socket is limited to 10 concurrent connections. It is
possible to change this value with "stats maxconn".

Binds a UNIX socket to <path> or a TCPv4/v6 address to <address:port>.
Connections to this socket will return various statistics outputs and even
allow some commands to be issued to change some runtime settings. Please
consult section 9.3 "Unix Socket commands" of Management Guide for more
details.

All parameters supported by "bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference" lines are supported, for instance to
restrict access to some users or their access rights. Please consult
section 5.1 for more information.

The default timeout on the stats socket is set to 10 seconds. It is possible
to change this value with "stats timeout". The value must be passed in
milliseconds, or be suffixed by a time unit among { us, ms, s, m, h, d }.

Path to a generated haproxy stats-file. On startup haproxy will preload the
values to its internal counters. Use the CLI command "dump stats-file" to
produce such stats-file. See the management manual for more details.

Activate alternative code to stress haproxy binary. Level is an integer from
0 to 9. The default value 0 disable any stressing execution. Levels from 1 to
9 will increase the stress pressure on the haproxy binary. Note that using
any positive level can significantly hurt performance. As such it should
never be activated unless for debugging purpose and on a developer request.

Makes process fail at startup when a setrlimit fails. HAProxy tries to set the
best setrlimit according to what has been calculated. If it fails, it will
emit a warning. This option is here to guarantee an explicit failure of
HAProxy when those limits fail. It is enabled by default. It may still be
forcibly disabled by prefixing it with the "no" keyword.

This setting is only available when support for threads was built in. It
enumerates the list of threads that will compose thread group <group>.
Thread numbers and group numbers start at 1. Thread ranges are defined either
using a single thread number at once, or by specifying the lower and upper
bounds delimited by a dash '-' (e.g. "1-16"). Unassigned threads will be
automatically assigned to unassigned thread groups, and thread groups
defined with this directive will never receive more threads than those
defined. Defining the same group multiple times overrides previous
definitions with the new one. See also "nbthread" and "thread-groups".

This setting is only available when support for threads was built in. It
makes HAProxy split its threads into <number> independent groups. At the
moment, the default value is 1. Thread groups make it possible to reduce
sharing between threads to limit contention, at the expense of some extra
configuration efforts. It is also the only way to use more than 64 threads
since up to 64 threads per group may be configured. The maximum number of
groups is configured at compile time and defaults to 16. See also "nbthread".

This setting is used to enforce a limit to the number of threads, either
detected, or configured. This is particularly useful on operating systems
where the number of threads is automatically detected, where a number of
threads lower than the number of CPUs is desired in generic and portable
configurations. Indeed, while "nbthread" enforces a number of threads that
will result in a warning and bad performance if higher than CPUs available,
thread-hard-limit will only cap the maximum value and automatically limit
the number of threads to no higher than this value, but will not raise lower
values. If "nbthread" is forced to a higher value, thread-hard-limit wins,
and a warning is emitted in so that the configuration anomaly can be
fixed. By default there is no limit. See also "nbthread".

Changes the process's user ID to <number>. It is recommended that the user ID
is dedicated to HAProxy or to a small set of similar daemons. HAProxy must
be started with superuser privileges in order to be able to switch to another
one. See also "gid
This keyword is available in sections :
Process management and security
Bind options" and "user
This keyword is available in sections :
Userlists
Process management and security
Bind options".

Sets the maximum number of per-process file-descriptors to <number>. By
default, it is automatically computed, so it is recommended not to use this
option. If the intent is only to limit the number of file descriptors, better
use "fd-hard-limit" instead.

Note that the dynamic servers are not taken into account in this automatic
resource calculation. If using a large number of them, it may be needed to
manually specify this value.

Fixes common settings to UNIX listening sockets declared in "bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference" statements.
This is mainly used to simplify declaration of those UNIX sockets and reduce
the risk of errors, since those settings are most commonly required but are
also process-specific. The <prefix> setting can be used to force all socket
path to be relative to that directory. This might be needed to access another
component's chroot. Note that those paths are resolved before HAProxy chroots
itself, so they are absolute. The <mode>, <user>, <uid>, <group> and <gid>
all have the same meaning as their homonyms used by the "bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference" statement. If
both are specified, the "bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference" statement has priority, meaning that the
"unix-bind" settings may be seen as process-wide default settings.

Removes environment variables specified in arguments. This can be useful to
hide some sensitive information that are occasionally inherited from the
user's environment during some operations. Variables which did not exist are
silently ignored so that after the operation, it is certain that none of
these variables remain. The changes immediately take effect so that the next
line in the configuration file will not see these variables. See also
"setenv", "presetenv", and "resetenv".

Similar to "uid
This keyword is available in sections :
Process management and security
Bind options" but uses the UID of user name <user name> from /etc/passwd.
See also "uid
This keyword is available in sections :
Process management and security
Bind options" and "group
This keyword is available in sections :
Userlists
Process management and security
Bind options".

Only letters, digits, hyphen and underscore are allowed, like in DNS names.

This statement is useful in HA configurations where two or more processes or
servers share the same IP address. By setting a different node-name on all
nodes, it becomes easy to immediately spot what server is handling the
traffic.

Sets the WURFL Useragent cache size. For faster lookups, already processed user
agents are kept in a LRU cache :
- "0"     : no cache is used.
- <size>  : size of lru cache in elements.

Please note that this option is only available when HAProxy has been compiled
with USE_WURFL=1.

The path of the WURFL data file to provide device detection services. The
file should be accessible by HAProxy with relevant permissions.

Please note that this option is only available when HAProxy has been compiled
with USE_WURFL=1.

A space-delimited list of WURFL capabilities, virtual capabilities, property
names we plan to use in injected headers. A full list of capability and
virtual capability names is available on the Scientiamobile website :

    https://www.scientiamobile.com/wurflCapability

Valid WURFL properties are:
- wurfl_id                    Contains the device ID of the matched device.

- wurfl_root_id               Contains the device root ID of the matched
                              device.

- wurfl_isdevroot             Tells if the matched device is a root device.
                              Possible values are "TRUE" or "FALSE".

- wurfl_useragent             The original useragent coming with this
                              particular web request.

- wurfl_api_version           Contains a string representing the currently
                              used Libwurfl API version.

- wurfl_info                  A string containing information on the parsed
                              wurfl.xml and its full path.

- wurfl_last_load_time        Contains the UNIX timestamp of the last time
                              WURFL has been loaded successfully.

- wurfl_normalized_useragent  The normalized useragent.

Please note that this option is only available when HAProxy has been compiled
with USE_WURFL=1.

A char that will be used to separate values in a response header containing
WURFL results. If not set that a comma (',') will be used by default.

Please note that this option is only available when HAProxy has been compiled
with USE_WURFL=1.

A list of WURFL patch file paths. Note that patches are loaded during startup
thus before the chroot.

Please note that this option is only available when HAProxy has been compiled
with USE_WURFL=1.

In some situations, especially when dealing with low latency on processors
supporting a variable frequency or when running inside virtual machines, each
time the process waits for an I/O using the poller, the processor goes back
to sleep or is offered to another VM for a long time, and it causes
excessively high latencies. This option provides a solution preventing the
processor from sleeping by always using a null timeout on the pollers. This
results in a significant latency reduction (30 to 100 microseconds observed)
at the expense of a risk to overheat the processor. It may even be used with
threads, in which case improperly bound threads may heavily conflict,
resulting in a worse performance and high values for the CPU stolen fields
in "show info" output, indicating which threads are misconfigured. It is
important not to let the process run on the same processor as the network
interrupts when this option is used. It is also better to avoid using it on
multiple CPU threads sharing the same core. This option is disabled by
default. If it has been enabled, it may still be forcibly disabled by
prefixing it with the "no" keyword. It is ignored by the "select" and
"poll" pollers.

This option is automatically disabled on old processes in the context of
seamless reload; it avoids too much cpu conflicts when multiple processes
stay around for some time waiting for the end of their current connections.

By default, HAProxy tries to spread the start of health checks across the
smallest health check interval of all the servers in a farm. The principle is
to avoid hammering services running on the same server. But when using large
check intervals (10 seconds or more), the last servers in the farm take some
time before starting to be tested, which can be a problem. This parameter is
used to enforce an upper bound on delay between the first and the last check,
even if the servers' check intervals are larger. When servers run with
shorter intervals, their intervals will be respected though.

Sets the maximum CPU usage HAProxy can reach before stopping the compression
for new requests or decreasing the compression level of current requests.
It works like 'maxcomprate' but measures CPU usage instead of incoming data
bandwidth. The value is expressed in percent of the CPU used by HAProxy. A
value of 100 disable the limit. The default value is 100. Setting a lower
value will prevent the compression work from slowing the whole process down
and from introducing high latencies.

Sets the maximum per-process input compression rate to <number> kilobytes
per second. For each stream, if the maximum is reached, the compression
level will be decreased during the stream. If the maximum is reached at the
beginning of a stream, the stream will not compress at all. If the maximum
is not reached, the compression level will be increased up to
tune.comp.maxlevel. A value of zero means there is no limit, this is the
default value.

Sets the maximum per-process number of concurrent connections to <number>. It
is equivalent to the command-line argument "-n". The value provided in
command-line argument via "-n" takes the precedence over the maxconn value set
in the global section. Haproxy process could be also compiled with
SYSTEM_MAXCONN compile-time variable, which is served in this case as the
system maxconn maximum. Again, the command-line "-n" argument allows at
runtime to bypass SYSTEM_MAXCONN limit, if set. Proxies will stop accepting
connections when maxconn is reached. The process soft file descriptor limit
(could be obtained with "ulimit -n" command) is automatically adjusted
according to provided maxconn. See also "ulimit-n". Note: the "select" poller
cannot reliably use more than 1024 file descriptors on some platforms. If your
platform only supports select and reports "select FAILED" on startup, you need
to reduce the maxconn until it works (slightly below 500 in general). If
maxconn value is not set, it will be automatically calculated based on the
current file descriptors limits, reported by the "ulimit -nH" command (we take
the maximum between the hard and soft values), then automatic value will be
possibly reduced by "fd-hard-limit" and by memory limit, if the latter was
enforced via "-m" command line option. Automatic value is also dependent from
the buffer size, memory allocated to compression, SSL cache size, and the use
or not of SSL and the associated maxsslconn (which can also be automatic).

Sets the maximum per-process number of connections per second to <number>.
Proxies will stop accepting connections when this limit is reached. It can be
used to limit the global capacity regardless of each frontend capacity. It is
important to note that this can only be used as a service protection measure,
as there will not necessarily be a fair share between frontends when the
limit is reached, so it's a good idea to also limit each frontend to some
value close to its expected share. Also, lowering tune.maxaccept can improve
fairness.

Sets the maximum per-process number of pipes to <number>. Currently, pipes
are only used by kernel-based tcp splicing. Since a pipe contains two file
descriptors, the "ulimit-n" value will be increased accordingly. The default
value is maxconn/4, which seems to be more than enough for most heavy usages.
The splice code dynamically allocates and releases pipes, and can fall back
to standard copy, so setting this value too low may only impact performance.

Sets the maximum per-process number of sessions per second to <number>.
Proxies will stop accepting connections when this limit is reached. It can be
used to limit the global capacity regardless of each frontend capacity. It is
important to note that this can only be used as a service protection measure,
as there will not necessarily be a fair share between frontends when the
limit is reached, so it's a good idea to also limit each frontend to some
value close to its expected share. Also, lowering tune.maxaccept can improve
fairness.

Sets the maximum per-process number of concurrent SSL connections to
<number>. By default there is no SSL-specific limit, which means that the
global maxconn setting will apply to all connections. Setting this limit
avoids having openssl use too much memory and crash when malloc returns NULL
(since it unfortunately does not reliably check for such conditions). Note
that the limit applies both to incoming and outgoing connections, so one
connection which is deciphered then ciphered accounts for 2 SSL connections.
If this value is not set, but a memory limit is enforced, this value will be
automatically computed based on the memory limit, maxconn,  the buffer size,
memory allocated to compression, SSL cache size, and use of SSL in either
frontends, backends or both. If neither maxconn nor maxsslconn are specified
when there is a memory limit, HAProxy will automatically adjust these values
so that 100% of the connections can be made over SSL with no risk, and will
consider the sides where it is enabled (frontend, backend, both).

Sets the maximum per-process number of SSL sessions per second to <number>.
SSL listeners will stop accepting connections when this limit is reached. It
can be used to limit the global SSL CPU usage regardless of each frontend
capacity. It is important to note that this can only be used as a service
protection measure, as there will not necessarily be a fair share between
frontends when the limit is reached, so it's a good idea to also limit each
frontend to some value close to its expected share. It is also important to
note that the sessions are accounted before they enter the SSL stack and not
after, which also protects the stack against bad handshakes. Also, lowering
tune.maxaccept can improve fairness.

Sets the maximum amount of RAM in megabytes per process usable by the zlib.
When the maximum amount is reached, future streams will not compress as long
as RAM is unavailable. When sets to 0, there is no limit.
The default value is 0. The value is available in bytes on the UNIX socket
with "show info" on the line "MaxZlibMemUsage", the memory used by zlib is
"ZlibMemUsage" in bytes.

Disables memory trimming ("malloc_trim") at a few moments where attempts are
made to reclaim lots of memory (on memory shortage or on reload). Trimming
memory forces the system's allocator to scan all unused areas and to release
them. This is generally seen as nice action to leave more available memory to
a new process while the old one is unlikely to make significant use of it.
But some systems dealing with tens to hundreds of thousands of concurrent
connections may experience a lot of memory fragmentation, that may render
this release operation extremely long. During this time, no more traffic
passes through the process, new connections are not accepted anymore, some
health checks may even fail, and the watchdog may even trigger and kill the
unresponsive process, leaving a huge core dump. If this ever happens, then it
is suggested to use this option to disable trimming and stop trying to be
nice with the new process. Note that advanced memory allocators usually do
not suffer from such a problem.

Disables the use of the "epoll" event polling system on Linux. It is
equivalent to the command-line argument "-de". The next polling system
used will generally be "poll". See also "nopoll".

Disables the use of the event ports event polling system on SunOS systems
derived from Solaris 10 and later. It is equivalent to the command-line
argument "-dv". The next polling system used will generally be "poll". See
also "nopoll".

Disables the use of getaddrinfo(3) for name resolving. It is equivalent to
the command line argument "-dG". Deprecated gethostbyname(3) will be used.

Disables the use of the "kqueue" event polling system on BSD. It is
equivalent to the command-line argument "-dk". The next polling system
used will generally be "poll". See also "nopoll".

Disables the use of ktls. It is equivalent to the command line argument
"-dT".

Disables the use of the "poll" event polling system. It is equivalent to the
command-line argument "-dp". The next polling system used will be "select".
It should never be needed to disable "poll" since it's available on all
platforms supported by HAProxy. See also "nokqueue", "noepoll" and
"noevports".

Disables the use of SO_REUSEPORT - see socket(7). It is equivalent to the
command line argument "-dR".

Disables the use of kernel tcp splicing between sockets on Linux. It is
equivalent to the command line argument "-dS". Data will then be copied
using conventional and more portable recv/send calls. Kernel tcp splicing is
limited to some very recent instances of kernel 2.6. Most versions between
2.6.25 and 2.6.28 are buggy and will forward corrupted data, so they must not
be used. This option makes it easier to globally disable kernel splicing in
case of doubt. See also "option splice-auto", "option splice-request" and
"option splice-response".

Enables ('on') or disables ('off') per-function memory profiling. This will
keep usage statistics of malloc/calloc/realloc/free calls anywhere in the
process (including libraries) which will be reported on the CLI using the
"show profiling" command. This is essentially meant to be used when an
abnormal memory usage is observed that cannot be explained by the pools and
other info are required. The performance hit will typically be around 1%,
maybe a bit more on highly threaded machines, so it is normally suitable for
use in production. The same may be achieved at run time on the CLI using the
"set profiling memory" command, please consult the management manual.

Enables ('on') or disables ('off') per-task CPU profiling. When set to 'auto'
the profiling automatically turns on a thread when it starts to suffer from
an average latency of 1000 microseconds or higher as reported in the
"avg_loop_us" activity field, and automatically turns off when the latency
returns below 990 microseconds (this value is an average over the last 1024
loops so it does not vary quickly and tends to significantly smooth short
spikes). It may also spontaneously trigger from time to time on overloaded
systems, containers, or virtual machines, or when the system swaps (which
must absolutely never happen on a load balancer).

When task profiling is enabled, HAProxy can also collect the time each task
spends with a lock held or waiting for a lock, as well as the time spent
waiting for a memory allocation to succeed in case of a pool cache miss. This
can sometimes help understand certain causes of latency. For this, the extra
keywords "lock" (to enable lock time collection), "no-lock" (to disable it),
"memory" (to enable memory allocation time collection) or "no-memory" (to
disable it) may additionally be passed. By default they are not enabled since
they can have a non-negligible CPU impact on highly loaded systems (3-10%).
Note that the overhead is only taken when profiling is effectively running,
so that when running in "auto" mode, it will only appear when HAProxy decides
to turn it on.

CPU profiling per task can be very convenient to report where the time is
spent and which requests have what effect on which other request. Enabling
it will typically affect the overall's performance by less than 1%, thus it
is recommended to leave it to the default 'auto' value so that it only
operates when a problem is identified. This feature requires a system
supporting the clock_gettime(2) syscall with clock identifiers
CLOCK_MONOTONIC and CLOCK_THREAD_CPUTIME_ID, otherwise the reported time will
be zero. This option may be changed at run time using "set profiling" on the
CLI.

Sometimes it is desirable to avoid sending agent and health checks to
servers at exact intervals, for instance when many logical servers are
located on the same physical server. With the help of this parameter, it
becomes possible to add some randomness in the check interval between 0
and +/- 50%. A value between 2 and 5 seems to show good results. The
default value remains at 0.

Sets the OpenSSL engine to <name>. List of valid values for <name> may be
obtained using the command "openssl engine". This statement may be used
multiple times, it will simply enable multiple crypto engines. Referencing an
unsupported engine will prevent HAProxy from starting. Note that many engines
will lead to lower HTTPS performance than pure software with recent
processors. The optional command "algo" sets the default algorithms an ENGINE
will supply using the OPENSSL function ENGINE_set_default_string(). A value
of "ALL" uses the engine for all cryptographic operations. If no list of
algo is specified then the value of "ALL" is used. A comma-separated list
of different algorithms may be specified, including: RSA, DSA, DH, EC, RAND,
CIPHERS, DIGESTS, PKEY, PKEY_CRYPTO, PKEY_ASN1. This is the same format that
openssl configuration file uses:
https://www.openssl.org/docs/man1.0.2/apps/config.html

HAProxy Version 2.6 disabled the support for engines in the default build.
This option is only available when HAProxy has been built with support for
it.  In case the ssl-engine is required HAProxy can be rebuild with the
USE_ENGINE=1 flag.

Adds SSL_MODE_ASYNC mode to the SSL context. This enables asynchronous TLS
I/O operations if asynchronous capable SSL engines are used. The current
implementation supports a maximum of 32 engines. The Openssl ASYNC API
doesn't support moving read/write buffers and is not compliant with
HAProxy's buffer management. So the asynchronous mode is disabled on
read/write  operations (it is only enabled during initial and renegotiation
handshakes).

Enables ('on') of disabled ('off') the zero-copy forwarding of data for the
applets. It is enabled by default.

Sets a hard limit on the number of buffers which may be allocated per process.
The default value is zero which means unlimited. The limit will automatically
be re-adjusted to satisfy the reserved buffers for emergency situations so
that the user doesn't have to perform complicated calculations. Forcing this
value can be particularly useful to limit the amount of memory a process may
take, while retaining a sane behavior. When this limit is reached, a task
that requests a buffer waits for another one to be released first. Most of
the time the waiting time is very short and not perceptible provided that
limits remain reasonable. However, some historical limitations have weakened
this mechanism over versions and it is known that in certain situations of
sustained shortage, some tasks may freeze until their timeout expires, so it
is safer to avoid using this when not strictly necessary.

Sets the number of per-thread buffers which are pre-allocated and reserved
for use only during memory shortage conditions resulting in failed memory
allocations. The minimum value is 0 and the default is 4. There is no reason
a user would want to change this value, unless a core developer suggests to
change it for a very specific reason.

Sets the buffer size to this size (in bytes). Lower values allow more
streams to coexist in the same amount of RAM, and higher values allow some
applications with very large cookies to work. The default value is 16384 and
can be changed at build time. It is strongly recommended not to change this
from the default value, as very low values will break some services such as
statistics, and values larger than default size will increase memory usage,
possibly causing the system to run out of memory. At least the global maxconn
parameter should be decreased by the same factor as this one is increased. In
addition, use of HTTP/2 mandates that this value must be 16384 or more. If an
HTTP request is larger than (tune.bufsize - tune.maxrewrite), HAProxy will
return HTTP 400 (Bad Request) error. Similarly if an HTTP response is larger
than this size, HAProxy will return HTTP 502 (Bad Gateway). Note that the
value set using this parameter will automatically be rounded up to the next
multiple of 8 on 32-bit machines and 16 on 64-bit machines.

Sets the size in bytes for large buffers. By defaults, support for large
buffers is not enabled, it must explicitly be enable by setting this value.

These buffers are designed to be used in some specific contexts where more
data must be bufferized without changing the size of regular buffers. The
large buffers are not implicitly used.

Note that when large buffers are configured, three special large buffers will
be allocated for each threads during startup for internal usage.

Sets the size in bytes for small buffers. The defaults value is 1024.

These buffers are designed to be used in some specific contexts where memory
consumption is restrained but it seems unnecessary to allocate a full buffer.
If however a small buffer is not sufficient, a reallocation is automatically
done to switch to a standard size buffer.

For the moment, it is automatically used only by HTTP/3 protocol to emit the
response headers. Otherwise, small buffers support can be enabled for
specific proxies via the "use-small-buffers" option.

Sets the maximum size allowed for the payload passed to a command on the CLI.

On the CLI, a command line is limited by the buffer size. It means all
commands and their arguments must fit in a buffer to be processed, excluding
the payload that can be passed to the last command of the command line. This
payload can be allocated into a dedicated area if necessary. Its size is
limited by this parameter. The default value is 128KB.

While it should be high enough for most usage, if this value is changed, it
must be carefully chosen. A huge value can have impact on the HAProxy
performance. Depending on the command, a huge payload can be quite long to
process and can possibly trigger the watchdog.

Please consult the management manual for details about the CLI.

Sets the maximum compression level. The compression level affects CPU
usage during compression. This value affects CPU usage during compression.
Each stream using compression initializes the compression algorithm with
this value. The default value is 1.

For dynamic backends support, all named defaults sections are now kept in
memory after parsing. This is necessary as backend added at runtime must be
based on a named defaults for its configuration.

This may consume significant memory if the number of defaults instances is
important. In this case and if dynamic backend feature is unnecessary, it's
possible to use this option to force deletion of defaults section after
parsing. It is still mandatory though to keep referenced defaults section
which contain settings whose cannot be copied by their referencing proxies.
For example, this is the case if the defaults section defines TCP/HTTP rules
or a tcpcheck ruleset.

Disables the data fast-forwarding. It is a mechanism to optimize the data
forwarding by passing data directly from a side to the other one without
waking the stream up. Thanks to this directive, it is possible to disable
this optimization. Note it also disable any kernel tcp splicing but also the
zero-copy forwarding. This command is not meant for regular use, it will
generally only be suggested by developers along complex debugging
sessions.

Globally disables the zero-copy forwarding of data. It is a mechanism to
optimize the data fast-forwarding by avoiding to use the channel's buffer.
Thanks to this directive, it is possible to disable this optimization. Note
it also disable any kernel tcp splicing.

Along HAProxy's history, a few complex issues were met that were caused by
bugs in the epoll mechanism in the Linux kernel. These ones usually are very
rare and unreproducible outside the reporter's environment, and may only be
worked around by disabling epoll and switching to poll instead, which is not
very satisfying for high performance environments. Each time, issues affect
only very specific (and rare) event types, and offering the ability to mask
them can constitute a more acceptable work-around. This options offers this
possibility by permitting to silently ignore events a few uncommon events
and replace them with an input (which reports an unspecified incoming event).
The effect is to avoid the fast error processing paths in certain places and
only use the common paths. This should never be used unless being invited to
do so by an expert in order to diagnose or work around a kernel bug.

The option takes a single argument which is a comma-delimited list of words
each designating an event to be masked. The currently supported list of
events is:
  - "err":   mask the EPOLLERR event
  - "hup":   mask the EPOLLHUP events
  - "rdhup": mask the EPOLLRDHUP events

# mask all non-traffic epoll events:
tune.epoll.mask-events err,hup,rdhup

Sets the number of events that may be processed at once by an asynchronous
task handler (from event_hdl API). <number> should be included between 1
and 10000. Large number could cause thread contention as a result of the
task doing heavy work without interruption, and on the other hand, small
number could result in the task being constantly rescheduled because it
cannot consume enough events per run and is not able to catch up with the
event producer. The default value may be forced at build time, otherwise
defaults to 100.

If compiled with DEBUG_FAIL_ALLOC or started with "-dMfail", gives the
percentage of chances an allocation attempt fails. Must be between 0 (no
failure) and 100 (no success). This is useful to debug and make sure memory
failures are handled gracefully. When not set, the ratio is 0. However the
command-line "-dMfail" option automatically sets it to 1% failure rate so that
it is not necessary to change the configuration for testing.

Enables ('on') or disables ('off') the edge-triggered polling mode for FDs
that support it. This is currently only support with epoll. It may noticeably
reduce the number of epoll_ctl() calls and slightly improve performance in
certain scenarios. This is still experimental, it may result in frozen
connections if bugs are still present, and is disabled by default.

Sets the minimum CPU usage between 0 and 100, at which connections showing
too many glitches will be killed. This applies to connections that have
reached their glitches-threshold limit. In environments where very long
connections often behave badly without causing any performance impact, it
might be desirable to keep them regardless of their misbehavior as long as
they do not hurt, and to only start to kill such connections when the CPU is
getting busy. This parameters allows to specify that a connection reaching
its glitches threshold will be actively killed when the CPU usage is at this
level or above, but never when it's below. Note that the CPU usage is
measured per thread, so a single misbehaving connection might be killed. The
default is zero, meaning that a connection reaching its glitches-threshold
will automatically get killed. A rule of thumb would be to set this value to
twice the usually observed CPU usage, or the commonly observed CPU usage plus
half the idle one (i.e. if CPU commonly reaches 60%, setting 80 here can make
sense). This parameter has no effect without tune.h2.fe.glitches-threshold,
tune.quic.fe.sec.glitches-threshold or tune.h1.fe.glitches-threshold. See
also the global parameters "tune.h2.fe.glitches-threshold",
"tune.h1.fe.glitches-threshold" and "tune.quic.fe.sec.glitches-threshold".

Sets the threshold for the number of glitches on a HTTP/1 backend connection,
after which that connection will automatically be killed. This allows to
automatically kill misbehaving connections without having to write explicit
rules for them. The default value is zero, indicating that no threshold is
set so that no event will cause a connection to be closed. Typical events
include improperly formatted headers that had been nevertheless accepted by
"accept-unsafe-violations-in-http-response". Any non-zero value here should
probably be in the hundreds or thousands to be effective without affecting
slightly bogus servers. It is also possible to only kill connections when the
CPU usage crosses a certain level, by using "tune.glitches.kill.cpu-usage".
Note that a graceful close is attempted at 75% of the configured threshold by
advertising a GOAWAY for a future stream. This ensures that a slightly faulty
connection will stop being used after some time without risking to interrupt
ongoing transfers.

Sets the threshold for the number of glitches on a HTTP/1 frontend connection
after which that connection will automatically be killed. This allows to
automatically kill misbehaving connections without having to write explicit
rules for them. The default value is zero, indicating that no threshold is
set so that no event will cause a connection to be closed. Typical events
include improperly formatted headers that had been nevertheless accepted by
"accept-unsafe-violations-in-http-request". Any non-zero value here should
probably be in the hundreds or thousands to be effective without affecting
slightly bogus clients. It is also possible to only kill connections when the
CPU usage crosses a certain level, by using "tune.glitches.kill.cpu-usage".
Note that a graceful close is attempted at 75% of the configured threshold by
advertising a GOAWAY for a future stream. This ensures that a slightly non-
compliant client will have the opportunity to create a new connection and
continue to work unaffected without ever triggering the hard close thus
risking to interrupt ongoing transfers.

Enables ('on') of disabled ('off') the zero-copy receives of data for the H1
multiplexer. It is enabled by default.

Enables ('on') of disabled ('off') the zero-copy sends of data for the H1
multiplexer. It is enabled by default.

Sets the threshold for the number of glitches on a backend connection, where
that connection will automatically be killed. This allows to automatically
kill misbehaving connections without having to write explicit rules for them.
The default value is zero, indicating that no threshold is set so that no
event will cause a connection to be closed. Beware that some H2 servers may
occasionally cause a few glitches over long lasting connection, so any non-
zero value here should probably be in the hundreds or thousands to be
effective without affecting slightly bogus servers. It is also possible to
only kill connections when the CPU usage crosses a certain level, by using
"tune.glitches.kill.cpu-usage". Note that a graceful close is attempted at
75% of the configured threshold by advertising a GOAWAY for a future stream.
This ensures that a slightly faulty connection will stop being used after
some time without risking to interrupt ongoing transfers.

Sets the HTTP/2 initial window size for outgoing connections, which is the
number of bytes the server can respond before waiting for an acknowledgment
from HAProxy. This setting only affects payload contents, not headers. When
not set, the common default value set by tune.h2.initial-window-size applies.
It can make sense to slightly increase this value to allow faster downloads
or to reduce CPU usage on the servers, at the expense of creating unfairness
between clients. It is better to use tune.h2.be.rxbuf instead, which does not
cause any unfairness. It doesn't affect resource usage.

Sets the HTTP/2 maximum number of concurrent streams per outgoing connection
(i.e. the number of outstanding requests on a single connection to a server).
When not set, the default set by tune.h2.max-concurrent-streams applies. A
smaller value than the default 100 may improve a site's responsiveness at the
expense of maintaining more established connections to the servers. When the
"http-reuse" setting is set to "always", it is recommended to reduce this
value so as not to mix too many different clients over the same connection,
because if a client is slower than others, a mechanism known as "head of
line blocking" tends to cause cascade effect on download speed for all
clients sharing a connection (keep tune.h2.be.initial-window-size low in this
case). It is highly recommended not to increase this value; some might find
it optimal to run at low values (1..5 typically).

Sets the maximum number of HTTP/2 incoming frames that will be processed at
once on a backend connection. It can be useful to set this to a low value
(a few tens to a few hundreds) when dealing with very large buffers in order
to maintain a low latency and a better fairness between multiple connections.
The default value is zero, which means that no limitation is enforced.

Sets the HTTP/2 receive buffer size for outgoing connections, in bytes. This
size will be rounded up to the next multiple of tune.bufsize and will be
shared between all streams uploading data (both HEADERS and DATA frames). In
any case, one buffer will always be granted to each stream, and 7/8 of the
unused buffers will be shared between streams downloading payload, allowing
to significantly improve upload performance and avoid head-of-line blocking
(HoL) on backend connections shared between multiple clients when http-reuse
is set to "always". The advertised per-stream window is automatically
adjusted to reflect the available space so that in practice it should not be
required to touch tune.h2.be.initial-window-size. If less than the size
required to deal with all streams is set, this minimum will be used. The
default value is about 1600k (100 streams with 16kB buffers each).

Sets the threshold for the number of glitches on a frontend connection, where
that connection will automatically be killed. This allows to automatically
kill misbehaving connections without having to write explicit rules for them.
The default value is zero, indicating that no threshold is set so that no
event will cause a connection to be closed. Beware that some H2 clientss may
occasionally cause a few glitches over long lasting connection, so any non-
zero value here should probably be in the hundreds or thousands to be
effective without affecting slightly bogus clients. It is also possible to
only kill connections when the CPU usage crosses a certain level, by using
"tune.glitches.kill.cpu-usage". Note that a graceful close is attempted at
75% of the configured threshold by advertising a GOAWAY for a future stream.
This ensures that a slightly non-compliant client will have the opportunity
to create a new connection and continue to work unaffected without ever
triggering the hard close thus risking to interrupt ongoing transfers.

Sets the HTTP/2 initial window size for incoming connections, which is the
number of bytes the client can upload before waiting for an acknowledgment
from HAProxy. This setting only affects payload contents (i.e. the body of
POST requests), not headers. When not set, the common default value set by
tune.h2.initial-window-size applies. It can make sense to increase this value
to allow faster uploads. The default value equals tune.bufsize (16384) and
allows at least 1.25 Mbps of bandwidth per stream over a 100 ms ping time,
and 125 Mbps for 1 ms ping time. It doesn't affect resource usage. Using too
large values may cause clients to experience a lack of responsiveness if
pages are accessed in parallel to large uploads. It is better to use
tune.h2.fe.rxbuf instead, which does not cause any unfairness.

Sets the HTTP/2 maximum number of concurrent streams per incoming connection
(i.e. the number of outstanding requests on a single connection from a
client). When not set, the default set by tune.h2.max-concurrent-streams
applies. A larger value than the default 100 may sometimes slightly improve
the page load time for complex sites with lots of small objects over high
latency networks but can also result in using more memory by allowing a
client to allocate more resources at once. The default value of 100 is
generally good and it is recommended not to change this value. A larger
concurrency also has an impact on the processing load and latency when
dealing with large numbers of connections which are themselves using many
streams, and it may lower the barrier to denial of service attacks. The
command supports the following optional arguments after the number:

- rq-load { <number> | auto | ignore }:
  The optional argument "rq-load" permits to dynamically adjust the
  advertised concurrency based on the executing thread's run-queue load:
  as long as the thread's load remains below the indicated threshold, the
  configured streams limit will be advertised. When the thread's load
  increases beyond the configured limit, the advertised streams limit will be
  decreased proportionally to the square of the excess ratio. Target load
  levels between 50 and 100 generally show very good moderation under heavy
  loads. Alternately, instead of specifying an explicit number, the keyword
  accepts "ignore", which is the default and means that the thread's
  run-queue load will not be considered to moderate the advertised streams
  limit, and "auto", which sets the limit to the "tune.runqueue-depth"
  value, which generally provides good results without having to tweak
  the configuration any further.

- min <number>:
  This sets the minimum advertised concurrency level when rq-load is used,
  even if this results in a higher load than the configured target. This
  allows to maintain a good level of interactivity on a site under very
  heavy load. The minimum and default value is 1, but values between 5
  and 15 can improve user experience.

tune.h2.fe.max-concurrent-streams 100 rq-load auto min 15

Sets the maximum number of HTTP/2 incoming frames that will be processed at
once on a frontend connection. It can be useful to set this to a low value
(a few tens to a few hundreds) when dealing with very large buffers in order
to maintain a low latency and a better fairness between multiple connections.
The default value is zero, which means that no limitation is enforced.

Sets the maximum number of HTTP/2 incoming RST_STREAM that will be processed
at once on a frontend connection. Once the specified number of RST_STREAM
frames are received, the connection handler will be placed in a low priority
queue and be processed after all other tasks. It can be useful to set this to
a very low value (1 or a few units) to significantly reduce the impacts of
RST_STREAM floods. RST_STREAM do happen when a user clicks on the Stop button
in their browser, but the few extra milliseconds caused by this requeuing are
generally unnoticeable, however they are generally effective at significantly
lowering the load caused from such floods. The default value is zero, which
means that no limitation is enforced.

Sets the HTTP/2 maximum number of total streams processed per incoming
connection. Once this limit is reached, HAProxy will send a graceful GOAWAY
frame informing the client that it will close the connection after all
pending streams have been closed. In practice, clients tend to close as fast
as possible when receiving this, and to establish a new connection for next
requests. Doing this is sometimes useful and desired in situations where
clients stay connected for a very long time and cause some imbalance inside a
farm. For example, in some highly dynamic environments, it is possible that
new load balancers are instantiated on the fly to adapt to a load increase,
and that once the load goes down they should be stopped without breaking
established connections. By setting a limit here, the connections will have
a limited lifetime and will be frequently renewed, with some possibly being
established to other nodes, so that existing resources are quickly released.

It's important to understand that there is an implicit relation between this
limit and "tune.h2.fe.max-concurrent-streams" above. Indeed, HAProxy will
always accept to process any possibly pending streams that might be in flight
between the client and the frontend, so the advertised limit will always
automatically be raised by the value configured in max-concurrent-streams,
and this value will serve as a hard limit above which a violation by a non-
compliant client will result in the connection being closed. Thus when
counting the number of requests per connection from the logs, any number
between max-total-streams and (max-total-streams + max-concurrent-streams)
may be observed depending on how fast streams are created by the client.

The default value is zero, which enforces no limit beyond those implied by
the protocol (2^30 ~= 1.07 billion). Values around 1000 may already cause
frequent connection renewal without causing any perceptible latency to most
clients. Setting it too low may result in an increase of CPU usage due to
frequent TLS reconnections, in addition to increased page load time. Please
note that some load testing tools do not support reconnections and may report
errors with this setting; as such it may be needed to disable it when running
performance benchmarks. See also "tune.h2.fe.max-concurrent-streams".

Sets the HTTP/2 receive buffer size for incoming connections, in bytes. This
size will be rounded up to the next multiple of tune.bufsize and will be
shared between all streams uploading data (both HEADERS and DATA frames). In
any case, one buffer will always be granted to each stream, and 7/8 of the
unused buffers will be shared between streams uploading payload, allowing to
significantly improve upload performance. The advertised per-stream window is
automatically adjusted to reflect the available space so that in practice it
should not be required to touch tune.h2.fe.initial-window-size. If less than
the size required to deal with all streams is set, this minimum will be used.
The default value of 1600k (100 streams with 16kB buffers each) permits
roughly 130 Mbps of upload speed for a client with a 100ms RTT.

Sets the HTTP/2 dynamic header table size. It defaults to 4096 bytes and
cannot be larger than 65536 bytes. A larger value may help certain clients
send more compact requests, depending on their capabilities. This amount of
memory is consumed for each HTTP/2 connection. It is recommended not to
change it.

Sets the default value for the HTTP/2 initial window size, on both incoming
and outgoing connections. This value is used for incoming connections when
tune.h2.fe.initial-window-size is not set, and by outgoing connections when
tune.h2.be.initial-window-size is not set. This setting is used both as the
initial value and as a minimum per stream. The default value equals 16384
(tune.bufsize), which for uploads roughly allows at least 1.25 Mbps of
bandwidth per stream over a network showing a 100 ms ping time, or 125 Mbps
over a 1-ms local network. When less receive buffers than the maximum are in
use, within the limits defined by tune.h2.be.rxbuf and tune.h2.fe.rxbuf,
unused buffers will be shared between receiving streams. As such there is
normally no point in changing this default setting. Given that changing this
default value will both increase upload speeds and cause more unfairness
between clients on downloads, it is recommended to instead use the side-
specific settings tune.h2.fe.initial-window-size and
tune.h2.be.initial-window-size.

Sets the level of errors in the H2 demultiplexer that will generate a log.
The default is "stream", which means that any decoding error encountered in
the demultiplexer will lead to the emission of a log. The "connection" value
indicates that only logs that result in invalidating the connection will
produce a log. Finally, "none" indicates that no decoding error will produce
any log. It is recommended to set at least "connection" in order to detect
protocol anomalies, even if this means temporarily switching to "none" during
difficult periods.

Sets the default HTTP/2 maximum number of concurrent streams per connection
(i.e. the number of outstanding requests on a single connection). This value
is used for incoming connections when tune.h2.fe.max-concurrent-streams is
not set, and for outgoing connections when tune.h2.be.max-concurrent-streams
is not set. The default value is 100. The impact varies depending on the side
so please see the two settings above for more details. It is recommended not
to use this setting and to switch to the per-side ones instead. A value of
zero disables the limit so a single client may create as many streams as
allocatable by HAProxy. It is highly recommended not to change this value.

Sets the HTTP/2 maximum frame size that HAProxy announces it is willing to
receive to its peers. The default value is the largest between 16384 and the
buffer size (tune.bufsize). In any case, HAProxy will not announce support
for frame sizes larger than buffers. The main purpose of this setting is to
allow to limit the maximum frame size setting when using large buffers. Too
large frame sizes might have performance impact or cause some peers to
misbehave. It is highly recommended not to change this value.

Enables ('on') of disabled ('off') the zero-copy sends of data for the H2
multiplexer. It is enabled by default.

Sets the maximum length of captured cookies. This is the maximum value that
the "capture cookie xxx len yyy" will be allowed to take, and any upper value
will automatically be truncated to this one. It is important not to set too
high a value because all cookie captures still allocate this size whatever
their configured value (they share a same pool). This value is per request
per response, so the memory allocated is twice this value per connection.
When not specified, the limit is set to 63 characters. It is recommended not
to change this value.

Sets the maximum length of request URI in logs. This prevents truncating long
request URIs with valuable query strings in log lines. This is not related
to syslog limits. If you increase this limit, you may also increase the
'log ... len yyy' parameter. Your syslog daemon may also need specific
configuration directives too.
The default value is 1024.

Sets the maximum number of headers allowed in received HTTP messages. When a
message comes with a number of headers greater than this value (including the
first line), it is rejected with a "400 Bad Request" status code for a
request, or "502 Bad Gateway" for a response. The default value is 101, which
is enough for all usages, considering that the widely deployed Apache server
uses the same limit. It can be useful to push this limit further to
temporarily allow a buggy application to work by the time it gets fixed. The
accepted range is 1..32767. Keep in mind that each new header consumes 32bits
of memory for each stream, so don't push this limit too high.

Note that HTTP/1.1 is a text protocol, so there is no special limit when the
message is sent. The limit during the message parsing is sufficient. HTTP/2
and HTTP/3 are binary protocols and require an encoding step. A limit is set
too when headers are encoded to comply to limitation imposed by the
protocols. This limit is large enough but not documented on purpose. The same
limit is applied on the first steps of the decoding for the same reason.

Controls sharing idle connection pools between threads for a same server.
It can be enabled for all threads in a same thread group ('on'), enabled for
all threads ('full') or disabled ('off'). The default is to share them
between threads in the same thread group ('on'), in order to minimize the
number of persistent connections to a server, and to optimize the connection
reuse rate. Sharing with threads from other thread groups can have a
performance impact, and is not enabled by default, but can be useful if
maximizing connection reuse is a priority. To help with debugging or when
suspecting a bug in HAProxy around connection reuse, it can be convenient to
forcefully disable this idle pool sharing between multiple threads,
and force this option to "off". It is strongly recommended against disabling
this option without setting a conservative value on "pool-low-conn" for all
servers relying on connection reuse to achieve a high performance level,
otherwise connections might be closed very often as the thread count
increases.

Sets the duration after which HAProxy will consider that an empty buffer is
probably associated with an idle stream. This is used to optimally adjust
some packet sizes while forwarding large and small data alternatively. The
decision to use splice() or to send large buffers in SSL is modulated by this
parameter. The value is in milliseconds between 0 and 65535. A value of zero
means that HAProxy will not try to detect idle streams. The default is 1000,
which seems to correctly detect end user pauses (e.g. read a page before
clicking). There should be no reason for changing this value. Please check
tune.ssl.maxrecord below.

Normally, all "bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference" lines will create a single shard, that is, a single
socket that all threads of the process will listen to. With many threads,
this is not very efficient, and may even induce some important overhead in
the kernel for updating the polling state or even distributing events to the
various threads. Modern operating systems support balancing of incoming
connections, a mechanism that will consist in permitting multiple sockets to
be bound to the same address and port, and to evenly distribute all incoming
connections to these sockets so that each thread only sees the connections
that are waiting in the socket it is bound to. This significantly reduces
kernel-side overhead and increases performance in the incoming connection
path. This is usually enabled in HAProxy using the "shards
This keyword is available in sections :
Peers declaration
Bind options" setting on "bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference"
lines, which defaults to 1, meaning that each listener will be unique in the
process. On systems with many processors, it may be more convenient to change
the default setting to "by-thread" in order to always create one listening
socket per thread, or "by-group" in order to always create one listening
socket per thread group. Be careful about the file descriptor usage with
"by-thread" as each listener will need as many sockets as there are threads.
Also some operating systems (e.g. FreeBSD) are limited to no more than 256
sockets on a same address. Note that "by-group" will remain equivalent to
"by-process" for default configurations involving a single thread group, and
will fall back to sharing the same socket on systems that do not support this
mechanism. The default is "by-group" with a fallback to "by-process" for
systems or socket families that do not support multiple bindings.

Enables ('on' / 'fair') or disables ('off') the listener's multi-queue accept
which spreads the incoming traffic to all threads a "bind
This keyword is available in sections :
Peers declaration
Log forwarding
Alphabetically sorted keywords reference" line is allowed to
run on instead of taking them for itself. This provides a smoother traffic
distribution and scales much better, especially in environments where threads
may be unevenly loaded due to external activity (network interrupts colliding
with one thread for example). The default mode, "on", optimizes the choice of
a thread by picking in a sample the one with the less connections. It is
often the best choice when connections are long-lived as it manages to keep
all threads busy. A second mode, "fair", instead cycles through all threads
regardless of their instant load level. It can be better suited for short-
lived connections, or on machines with very large numbers of threads where
the probability to find the least loaded thread with the first mode is low.
Finally it is possible to forcefully disable the redistribution mechanism
using "off" for troubleshooting, or for situations where connections are
short-lived and it is estimated that the operating system already provides a
good enough distribution. The default is "on".

Explicitly tell haproxy how haproxy sample objects should be handled when
pushed to Lua. Indeed, when leveraging native converters, sample fetches or
variables from Lua script (to name a few), haproxy converts the internal
smp type to equivalent Lua type. Because of historical implementation, there
is an ambiguity around boolean handling: when doing Lua -> haproxy smp
conversion, booleans are properly preserved, but when doing haproxy
smp -> Lua conversion, booleans were converted to integers by mistake. This
means that a sample fetch or converter returning a boolean would return an
integer 0 or 1 when leveraged from Lua. Unfortunately, in Lua, booleans and
integers are not interchangeable. Thus, to avoid ambiguities,
"tune.lua.bool-sample-conversion" must explicitly be set to either "normal"
(which means dropping the historical behavior for better consistency) or
"pre-3.1-bug" (enforce historical behavior to prevent existing script logic
from misbehaving). If the option is not set explicitly and a Lua script is
loaded from the configuration, haproxy will emit a warning, and the option
will implicitly default to "pre-3.1-bug" to match with the historical
behavior. It is recommended to set this option to "normal" after ensuring
that in-use Lua scripts are properly handling bool haproxy samples as booleans.

This setting must be set before any "lua-load" or "lua-load-per-thread"
directive for it to be considered, else it is ignored.

The "burst" execution timeout applies to any Lua handler. If the handler
fails to finish or yield before timeout is reached, it will be aborted to
prevent thread contention, to prevent traffic from not being served for too
long, and ultimately to prevent the process from crashing because of the
watchdog kicking in. Unlike other lua timeouts which are yield-cumulative,
burst-timeout will ensure that the time spent in a single lua execution
window does not exceed the configured timeout.

Yielding here means that the lua execution is effectively interrupted
either through an explicit call to lua-yielding function such as
core.(m)sleep() or core.yield(), or following an automatic forced-yield
(see tune.lua.forced-yield) and that it will be resumed later when the
related task is set for rescheduling. Not all lua handlers may yield: we have
to make a distinction between yieldable handlers and unyieldable handlers.

For yieldable handlers (tasks, actions..), reaching the timeout means
"tune.lua.forced-yield" might be too high for the system, reducing it
could improve the situation, but it could also be a good idea to check if
adding manual yields at some key points within the lua function helps or not.
It may also indicate that the handler is spending too much time in a specific
lua library function that cannot be interrupted.

For unyieldable handlers (lua converters, sample fetches), it could simply
indicate that the handler is doing too much computation, which could result
from an improper design given that such handlers, which often block the
request execution flow, are expected to terminate quickly to allow the
request processing to go through. A common resolution approach here would be
to try to better optimize the lua function for speed since decreasing
"tune.lua.forced-yield" won't help.

This timeout only counts the pure Lua runtime. If the Lua does a core.sleep,
the sleeping time is not taken in account. The default timeout is 1000ms.

Note: if a lua GC cycle is initiated from the handler (either explicitly
requested or automatically triggered by lua after some time), the GC cycle
time will also be accounted for.

Indeed, there is no way to deduce the GC cycle time, so this could lead to
some false positives on saturated systems (where GC is having hard time to
catch up and consumes most of the available execution runtime). If it were
to be the case, here are some resolution leads:

  - checking if the script could be optimized to reduce lua memory footprint
  - fine-tuning lua GC parameters and / or requesting manual GC cycles
    (see: https://www.lua.org/manual/5.4/manual.html#pdf-collectgarbage)
  - increasing tune.lua.burst-timeout

Setting value to 0 completely disables this protection.

This directive forces the Lua engine to execute a yield each <number> of
instructions executed. This permits interrupting a long script and allows the
HAProxy scheduler to process other tasks like accepting connections or
forwarding traffic. The default value is 10000 instructions for scripts loaded
using "lua-load-per-thread" and MAX(500, 10000 / nbthread) instructions for
scripts loaded using "lua-load" (it was found to be an optimal value for
performance while taking care of not creating thread contention with multiple
threads competing for the global lua lock).

If HAProxy often executes some Lua code but more responsiveness is required,
this value can be lowered. If the Lua code is quite long and its result is
absolutely required to process the data, the <number> can be increased, but
the value should be set wisely as in multithreading context it could increase
contention.

Enables ('on') or disables ('off') logging the output of LUA scripts via the
loggers applicable to the current proxy, if any.

Defaults to 'on'.

Enables ('on') or disables ('off') logging the output of LUA scripts via
stderr.
When set to 'auto', logging via stderr is conditionally 'on' if any of:

  - tune.lua.log.loggers is set to 'off'
  - the script is executed in a non-proxy context with no global logger
  - the script is executed in a proxy context with no logger attached

Please note that, when enabled, this logging is in addition to the logging
configured via tune.lua.log.loggers.

Defaults to 'auto'.

Sets the maximum amount of RAM in megabytes per process usable by Lua. By
default it is zero which means unlimited. It is important to set a limit to
ensure that a bug in a script will not result in the system running out of
memory.

Selects which Lua standard libraries are loaded when initialising the Lua
state. The argument is a comma-separated list of library names taken from
the following set: table, io, os, string, math, utf8, package, debug. The
special values "all" and "none" may be used instead of a list. "none"
cannot be combined with library names. The default value is "all".

The base and coroutine libraries are always loaded regardless of this
setting: base provides core Lua functions that HAProxy relies on, and
coroutine is required because HAProxy overrides coroutine.create() with
its own safe implementation.

Note that fork() and new thread creation are already blocked by default in
HAProxy regardless of this setting, and can only be re-enabled via the
"insecure-fork-wanted" global directive. Restricting the set of loaded
libraries further reduces the attack surface exposed to Lua scripts. In
particular:
  - omitting "os" prevents os.execute() and os.exit()
  - omitting "io" prevents io.open() and io.popen()
  - omitting "package" prevents loading native C modules via require()
  - omitting "debug" prevents introspection of HAProxy internals via
    debug.getupvalue(), debug.getmetatable(), or debug.sethook()

tune.lua.openlibs none                    # only base + coroutine
tune.lua.openlibs string,math,table,utf8  # safe subset, no I/O or OS
tune.lua.openlibs all                     # default, load everything

This setting must be set before any "lua-load", "lua-load-per-thread" or
"lua-prepend-path" directive, otherwise a parse error is returned.

This is the execution timeout for the Lua services. This is useful for
preventing infinite loops or spending too much time in Lua. This timeout
counts only the pure Lua runtime. If the Lua does a sleep, the sleep is
not taken in account. The default timeout is 4s.

This is the execution timeout for the Lua sessions. This is useful for
preventing infinite loops or spending too much time in Lua. This timeout
counts only the pure Lua runtime. If the Lua does a sleep, the sleep is
not taken in account. The default timeout is 4s.

Purpose is the same as "tune.lua.session-timeout", but this timeout is
dedicated to the tasks. By default, this timeout isn't set because a task may
remain alive during of the lifetime of HAProxy. For example, a task used to
check servers.

Sets the number of active checks per thread above which a thread will
actively try to search a less loaded thread to run the health check, or
queue it until the number of active checks running on it diminishes. The
default value is zero, meaning no such limit is set. It may be needed in
certain environments running an extremely large number of expensive checks
with many threads when the load appears unequal and may make health checks
to randomly time out on startup, typically when using OpenSSL 3.0 which is
about 20 times more CPU-intensive on health checks than older ones. This will
have for result to try to level the health check work across all threads. The
vast majority of configurations do not need to touch this parameter. Please
note that too low values may significantly slow down the health checking if
checks are slow to execute.

Sets the maximum number of consecutive connections a process may accept in a
row before switching to other work. In single process mode, higher numbers
used to give better performance at high connection rates, though this is not
the case anymore with the multi-queue. This value applies individually to
each listener, so that the number of processes a listener is bound to is
taken into account. This value defaults to 4 which showed best results. If a
significantly higher value was inherited from an ancient config, it might be
worth removing it as it will both increase performance and lower response
time. In multi-process mode, it is divided by twice the number of processes
the listener is bound to. Setting this value to -1 completely disables the
limitation. It should normally not be needed to tweak this value.

Sets the maximum amount of events that can be processed at once in a call to
the polling system. The default value is adapted to the operating system. It
has been noticed that reducing it below 200 tends to slightly decrease
latency at the expense of network bandwidth, and increasing it above 200
tends to trade latency for slightly increased bandwidth. The configured value
must be lower than or equal to 1000000.

Sets the reserved buffer space to this size in bytes. The reserved space is
used for header rewriting or appending. The first reads on sockets will never
fill more than bufsize-maxrewrite. Historically it has defaulted to half of
bufsize, though that does not make much sense since there are rarely large
numbers of headers to add. Setting it too high prevents processing of large
requests or responses. Setting it too low prevents addition of new headers
to already large requests or to POST requests. It is generally wise to set it
to about 1024. It is automatically readjusted to half of bufsize if it is
larger than that. This means you don't have to worry about it when changing
bufsize.

Sets the maximum number of rules that can be evaluated at once in ruleset
evaluating functions, provided that they support yielding. Indeed, it is
not rare to see configurations with a large number of "tcp-request content"
or "http-request" rules for instance. A large number of rules combined with
cpu-demanding actions (e.g.: actions that work on content) may create thread
contention as all the rules from a given ruleset are evaluated under the same
polling loop if the evaluation is not interrupted. This option ensures that no
more than <number> number of rules may be executed under the same polling
loop for content-oriented rulesets (those that already support yielding due
to content inspection). What it does is that it forces the evaluating function
to yield, so that it comes back on the next polling loop to continues the
evaluation.

Affected rulesets are:
 - "tcp-request content"
 - "tcp-response content"
 - "http-request"
 - "http-response"

The default value is 50.

Sets the per-thread amount of memory that will be kept hot in the local cache
and will never be recoverable by other threads. Access to this memory is very
fast (lockless), and having enough is critical to maintain a good performance
level under extreme thread contention. The value is expressed in bytes, and
the default value is configured at build time via CONFIG_HAP_POOL_CACHE_SIZE
which defaults to 524288 (512 kB). A larger value may increase performance in
some usage scenarios, especially when performance profiles show that memory
allocation is stressed a lot. Experience shows that a good value sits between
once to twice the per CPU core L2 cache size. Too large values will have a
negative impact on performance by making inefficient use of the L3 caches in
the CPUs, and will consume larger amounts of memory. It is recommended not to
change this value, or to proceed in small increments. In order to completely
disable the per-thread CPU caches, using a very small value could work, but
it is better to use "-dMno-cache" on the command-line.

Adjusts the kernel's per-socket buffering so as to report that the sending
side of a socket is full once the amount of buffered data equals this value
plus the measured window size. The principle is to let the strict minimum
needed amount of bytes in socket buffers, plus a small margin corresponding
to what would be sent by the time haproxy tries to send again. Setting this
to a low value (typically around tune.bufsize) allows to significantly reduce
the memory consumption in system buffers, and reduce the application level
latency incurred by flushing buffered data. This generally represents a more
effective and more accurate setting than tune.sndbuf.client and
tune.sndbuf.client for systems supporting it. This applies per connection
(connection from a client or connection to a server depending on the setting)
and is only used by TCP connections. The default is zero, which means
unlimited. This is only available on Linux.

Sets the size of the pattern lookup cache to <number> entries. This is an LRU
cache which reminds previous lookups and their results. It is used by ACLs
and maps on slow pattern lookups, namely the ones using the "sub", "reg",
"dir", "dom", "end", "bin" match methods as well as the case-insensitive
strings. It applies to pattern expressions which means that it will be able
to memorize the result of a lookup among all the patterns specified on a
configuration line (including all those loaded from files). It automatically
invalidates entries which are updated using HTTP actions or on the CLI. The
default cache size is set to 10000 entries, which limits its footprint to
about 5 MB per process/thread on 32-bit systems and 8 MB per process/thread
on 64-bit systems, as caches are thread/process local. There is a very low
risk of collision in this cache, which is in the order of the size of the
cache divided by 2^64. Typically, at 10000 requests per second with the
default cache size of 10000 entries, there's 1% chance that a brute force
attack could cause a single collision after 60 years, or 0.1% after 6 years.
This is considered much lower than the risk of a memory corruption caused by
aging components. If this is not acceptable, the cache can be disabled by
setting this parameter to 0.

Sets the maximum number of stick-table updates that haproxy will try to
process at once when sending messages. Retrieving the data for these updates
requires some locking operations which can be CPU intensive on highly
threaded machines if unbound, and may also increase the traffic latency
during the initial batched transfer between an older and a newer process.
Conversely low values may also incur higher CPU overhead, and take longer
to complete. The default value is 200 and it is suggested not to change it.

Sets the kernel pipe buffer size to this size (in bytes). By default, pipes
are the default size for the system. But sometimes when using TCP splicing,
it can improve performance to increase pipe sizes, especially if it is
suspected that pipes are not filled and that many calls to splice() are
performed. This has an impact on the kernel's memory footprint, so this must
not be changed if impacts are not understood.

This setting sets the max number of file descriptors (in percentage) used by
HAProxy globally against the maximum number of file descriptors HAProxy can
use before we start killing idle connections when we can't reuse a connection
and we have to create a new one. The default is 25 (one quarter of the file
descriptor will mean that roughly half of the maximum front connections can
keep an idle connection behind, anything beyond this probably doesn't make
much sense in the general case when targeting connection reuse).

This setting sets the max number of file descriptors (in percentage) used by
HAProxy globally against the maximum number of file descriptors HAProxy can
use before we stop putting connection into the idle pool for reuse. The
default is 20.

Enables ('on') of disabled ('off') the zero-copy forwarding of data for the
pass-through multiplexer. To be used, the kernel splicing must also be
configured. It is enabled by default.

Defines how many lost packets are needed for the Cubic congestion control
algorithm to really consider a loss event. Normally, any loss event is
considered as the result of a congestion and is sufficient for Cubic to
restart from a smaller window. But experiments show that there can be a
variety of causes for losses that are not at all caused by congestion and
that can simply be qualified of spurious losses, and for which adjusting the
window will have no effect, except slowing communication down. Poor radio
signal, out-of-order delivery, high CPU usage on a client causing random
delays, as well as system timer imprecision can be among the common causes
for this. This setting allows to make Cubic a bit more tolerant to spurious
losses, by changing the minimum number of cumulated losses between two ACKs
to be considered as a loss event, which defaults to 1. Some significant gains
have been observed experimentally, but always accompanied with an aggravation
of the bandwidth wasted on retransmits, and an increased risk of saturation
of congested links. The value 2 may be used for short periods of time to
compare some metrics. Never go beyond 2 without an expert's prior analysis of
the situation. The default and minimum value is 1. Always use 1.

This keyword has been deprecated in 3.3 and will be removed in 3.5. It is
part of the streamlining process apply on QUIC configuration. If used, this
setting will only be applied on frontend connections.

Enables ('on') or disabled ('off') the HyStart++ (RFC 9406) algorithm for
QUIC connections used as a replacement for the slow start phase of congestion
control algorithms which may cause high packet loss. It is disabled by default.

This keyword has been deprecated in 3.3 and will be removed in 3.5. It is
part of the streamlining process apply on QUIC configuration. If used, this
setting will only be applied on frontend connections.

Sets the limit for which a single QUIC frame can be marked as lost. If
exceeded, the connection is considered as failing and is closed immediately.

The default value is 10.

This keyword has been deprecated in 3.3 and will be removed in 3.5. It is
part of the streamlining process apply on QUIC configuration. If used, this
setting will only be applied on frontend connections.

Sets the default maximum window size for the congestion controller of a
single QUIC connection either on frontend or backend side. The value must be
written as an integer with an optional suffix 'k', 'm' or 'g'. It must be
between 10k and 4g.

QUIC multiplexer also uses the current congestion window size to determine if
it can allocate new stream buffers on data emission. As such, the maximum
congestion window size also serves as a limit on this allocator.

The default value is 480k.

See also the "quic-cc-algo
This keyword is available in sections :
Bind options
Server and default-server options" bind and server options.

This keyword has been deprecated in 3.3 and will be removed in 3.5. It is
part of the streamlining process apply on QUIC configuration. If used, this
setting will only be applied on frontend connections.

The ratio applied to the packet reordering threshold calculated. It may
trigger a high packet loss detection when too small.

The default value is 50.

This keyword has been deprecated in 3.3 and will be removed in 3.5. It is
part of the streamlining process apply on QUIC configuration. If used, this
setting will only be applied on frontend connections.

Sets the QUIC max_idle_timeout transport parameters on either frontend or
backend side. It follows the HAProxy time format and is expressed in
milliseconds. This determines the period of time after which a connection is
silently closed if it has remained inactive during an effective period of
time. Both endpoints relies on the same negotiated value :
  - the minimum of the two parameters if both are not null,
  - the maximum if only one of them is not null,
  - if both parameters are null, this feature is disabled.

The default value is 30s.

This keyword has been deprecated in 3.3 and will be removed in 3.5. It is
part of the streamlining process apply on QUIC configuration. If used, this
setting will only be applied on frontend connections.

Sets the threshold for the number of glitches per connection either on
frontend or backend side, where that connection will automatically be killed.
This allows to automatically kill misbehaving connections without having to
write explicit rules for them. The default value is zero, indicating that no
threshold is set so that no event will cause a connection to be closed.
Beware that some QUIC clients may occasionally cause a few glitches over long
lasting connection, so any non- zero value here should probably be in the
hundreds or thousands to be effective without affecting slightly bogus
clients. It is also possible to only kill connections when the CPU usage
crosses a certain level, by using "tune.glitches.kill.cpu-usage".