Jannik Arndt

Italian phrases for everyday life 🇮🇹

After six weeks in Palermo, these are the words and phrases I use almost every day. So if you’re preparing for a trip to Italy, this is a good start!

My first two weeks in Palermo ☀️

The first two weeks of my two months in Palermo are almost over, and I learned a lot.

Moving from Hamburg to Palermo ☀️

I left the cold and dark Hamburg winter and escaped to Palermo for two months. Here’s how it started!

Finding yourself on the Safe Browsing List — a Post Mortem

This week we woke up to customer reports that they couldn’t reach their “Public Portal” (a way to share their roadmap) anymore. Instead, a red page with a huge warning told them “Deceptive site ahead”. What had happened?

Why growth is so bad

Over the past year, many (including me) have left the company I worked for for more or less growth-related reasons. But what is it about growth that actually drives people away? Step 1: need for workforce / talent The first growth isn’t bad. You can only do so much in a day, and at some point, your company will need more people to solve all the tasks. Or specialized people, because you…

Comparison of Chart Libraries for SwiftUI

Update, 2026: Apple released a native Charts framework at WWDC 2022. You probably don’t need any of the libraries compared here — start there first. The rest of this post reflects the options available in 2021. I want to add charts to my SwiftUI iOS App, Zettl . For that, I am going to compare the following libraries: ivanschuetz/SwiftCharts denniscm190/stock-charts…

Generating Open Graph Images for my Blog

Things Developers are and aren't Good at

…in my experience.

def and var in traits on Scala 2.12, 2.13 and 3.0.0

Scala trait s should define def s, because “A val can override a def, but a def cannot override a val” (via Alvin Alexander via StackOverflow ). But it’s interesting to look at how the compiler treats that. Alvin Alexander did that , but only for Scala 2.12.8. Let’s have a look at 2.12, 2.13 and the just released 3.0 (formerly known as dotty).

April Fools': “We rewrote it in Rust” or How To Fake A GitHub Repo

We recently had another team rewrite their service in Rust, with a massive boost in performance. So naturally, for April Fools’ I made a big announcement that our team followed suit: But, at good prank isn’t just “I thought this was true, but it wasn’t”. It’s “I though it was a joke, but for a brief moment doubted that”. The “Oh, no, he…

Using scalap, javap and the scala compiler to understand the journey from code to bytecode

Do you know what happens after you compile? Let’s take a look at what the Scala compiler tells us, and what scalap and javap can reveal about .class files.

Exception-Proof For-Comprehensions

I recently created a wonderful bug.

oAuth2 with Akka HTTP

This is a basic example how to implement oAuth2 using Akka HTTP and Scala. It provides three endpoints. From the clients point of view: / — publicly accessible, returns “Welcome!”, /auth — provide your username and password , receive an access_token in return, /api — secured by oAuth, send the access_token in a header to gain access. From the server’s point of view: / — publicly accessible,…

Akka HTTP on Heroku

Getting a Akka HTTP-based backend up and running on Heroku for free can be done in less then 30 minutes — if you know the tricks.

How to Write and Test a Reactive Reader for AWS SQS Using akka, alpakka and Localstack

This example show how to write a reactive reader for the AWS Simple Queue Service , using Scala and alpakka (respective akka streams).

How Event Sourcing in Akka Persistent Actors Works

While the Akka documentation is incredibly well written, it has surprisingly few images. Since I visualize concepts to remember them, here is my take on how Event Sourcing in Akka Persistence works:

Rotating PostgreSQL Passwords with no downtime

Changing the password for a PostgreSQL database user involves two steps: The change in the database and the change in the application code. This blog post describes how to do this without any downtime or failed authentication tries.

Examining a PostgreSQL with psql or pgcli

The PostgreSQL installation comes with a great tool, psql , to administer and inspect the database. pgcli extends this with syntax highlighting and autocompletion.

Using your Apple Watch Workout to Geotag DSLR Photos

I want my photos to have location info in them, and Nikon wants way too much money for that. So I’ll do this: Let my Apple Watch track where I go, using the Outdoor Walk , export the route as GPX and use exiftool to tag all my images. Here’s how I do that.

3 Ways How Passwords Get Leaked

You don’t need to “get hacked” to have your security compromised. Often enough you’ll do it yourself. The best way to prevent this is knowing when to be cautious.

Kirschblütenfeuerwerk

Russische Kirche, Fernsehturm, Landungsbrücken

Boberg

Alsterpanorama

Hochwasserbassin

How to add an SSH Key as a Kubernetes Secret

Adding an ssh-file as a secret sounds easy, but there are pitfalls.

Lazy Aliases in my Shell

I reduced the startup time of my shell by one second. Here’s how: What I do I work a lot with the shell (or “Terminal” app on MacOS), mostly kubectl , git , terraform and docker . And of course I use the absolutely best shell of all, oh-my-zsh . The Problem I noticed that recently the startup time for a new shell (or new tab) has grown longer than a second. That’s annoying, because…

How to use a Raspberry Pi for your Time Machine backups

Apples Time Machine is a great backup solution, you only have to do one thing: Connect your disk from time to time. Since that is way harder than it sounds, there’s a second option: Buy a 329€ Time Capsule and do backups over wifi! That’s too expensive? Here’s how to build your own Time Capsule with a Raspberry Pi 3 and an external hard drive.

How to install Tasmota on a Sonoff device without opening it

Update, 2026: The SonOTA flashing method described here is deprecated. The Tasmota project now has a web installer that’s simpler and doesn’t require any of this. The rest of this post reflects how it worked in 2018. Sonoff takes the standard ESP8266 chip and adds two things: a casing with wifi and great connectors and a custom OS and an app to control the devices. Unfortunately, the…

How to use a Raspberry Pi 3 with Apple Home

Update, 2026: Apple’s Home architecture has changed significantly since 2018. Homebridge still exists and still works, but the setup has evolved. Check homebridge.io for current instructions. The rest of this post reflects how it worked in 2018. “Hey Siri, turn on the bedroom lights!” I want that. Here’s how I did it: I bought a bunch of Sonoff devices (5€ each, 10€ for a light…

How to setup a Raspberry Pi 3 headless, without monitor, mouse or keyboard

I bought a raspberry pi as a smart home automation server. Here’s how to set it up without connecting a monitor, mouse or keyboard. All you need is an ethernet cable.

Terraform on Google Cloud Engine Quickstart

This is a quickstart for building something on Google Compute Engine without clicking any buttons (after you created the project).

Lessons learned in 2017

#1 Conway’s Law “organizations which design systems … are constrained to produce designs which are copies of the communication structures of these organizations.” So true.

What settings yield the sharpest landscape photo?

I was quite surprised at how difficult it is to get absolutely razor sharp images out of a very good (high-end-consumer/semi-pro) DSLR camera, namely the Nikon D7100. So I made the test: What settings in terms of aperture, shutter speed and ISO yield the sharpest landscape image?

Hamburg as seen from the Michel

Releasing a Scala + Maven project to Maven Central (Sonatype OSS)

If you write Scala in a Java-centric environment, chances are you might wind up with a Maven project, defined in a pom.xml . While this can work, it brings a few extra caveats if you want to submit your project to Maven Central (aka Sonatype OSSRH ). Step 1: Claim your Group ID When you first publish something to the Sonatype OSSRH, you have to create a JIRA account and then create a ticket for a…

Writing case classes to MongoDB in Scala

Storing case classes in a MongoDB database is incredibly easy, once you know how. The same goes for java.time classes such as ZonedDateTime , LocalDate or Duration . This example uses the official Mongo Scala Driver in version 2.x and the bsoncodec project by Ralph Schaer .

VERY Quick Start: Terraform

This post contains the absolut essence from the Terraform Getting Started Guide: https://www.terraform.io/intro/getting-started/install.html

Where bad code comes from

Ever wondered where bad code comes from? “This story is done” “Shouldn’t someone review it first?” “Oh, yeah … erm … I’ll do a quick refactoring first and then…” …when that other person is on holiday!

Storing sparse, key-value-like data in a relational database

Some ideas seem great at first but turn out to be incredibly bad in hindsight. I reviewed such an idea today.

Tough Mudder Norddeutschland 2017

A Minor Story Live at Methfesselfest

Git in one Image

I tried to create a single image that contains all the most important git commands:

The real world doesn't care about encoding

Last week one of our programs failed looking up an airplane by its registration . That’s not a surprise, since ac regs are a horrible identifier. They change all the time. Also there is almost no naming rule at all. Wikipedia states When painted on the fuselage, the prefix and suffix are usually separated by a dash (for example, YR-BMA ). When entered in a flight plan, the dash is omitted…

Belugas at Finkenwerder

My favourite animal: The Beluga!

Deploying Pentaho jobs into Production

TL;DR: You don’t. We eventually gave up on it. My personal lessons-learned: Pentaho Kettle (or “Community Edition”, CE, i.e. the open-source core) is a great product for one-time data transfer or on-demand data transfer, but not for resilient, scheduled jobs. The “Enterprise Edition” (EE) adds scheduling that doesn’t work reliably, and a very powerless server. Kerberos is a bitch.

Extracting Dimensions from an Oracle Database Table

Task You have a denormalized table and want to extract a column into a dimension table. Caveat You have to keep the ids. Extra-Caveat You use an Oracle database.

Lessons learned in 2016

#1 Do not fix your code. Rather understand why nothing kept you from creating this bug. Make your code so easy that this bug would have been obvious the first time.

Perfect Home Screen Layout

Being the IT-guy aka personal first-level-support ™ for way more people than I am comfortable with, I have held quite a few mobile phones in my hand and stared into the abyss that is their home screen. The home screen is the modern view into someone’s soul. In a post-privacy-world it is probably one of the most private things we have, since it is utterly worthless to someone who does not…

Bug Fixing in Production

(via I Love Programming ) Thank goodness, we don’t do production .