Engineering notes by Jumpei Ueno: AWS/GCP infrastructure, FinOps, SRE, CI/CD.
I build explainer videos fully automatically. For each scene, a local image-generation AI draws that moment, one frame at a time. I was making one about an ancient Roman general — the whole life of a…
I let an AI agent run the social media for my own product. The first thing I handed over was "post from our own account." Honestly, that part isn't that scary. The words are ours, and if it flops, we…
I run an AI agent (Claude Code) that produces content and takes it all the way to publishing on external platforms, on its own. I had exactly one rule. Publishing is irreversible, so right before it…
The scariest moment I've had while talking design with an AI wasn't a code bug. It wasn't a prompt gone sideways. It was this: the AI (and honestly, me too) had quietly decided "this data is fine to…
I'm building an app with Claude Code right now. The setup is a little unusual. One "commander" session writes the instructions, and separate "worker" sessions implement them in parallel. The commande…
I run an automated video pipeline that generates images locally, on my Mac. A 16GB M4. The image model is FLUX, a 12B-parameter thing that keeps 7GB of weights resident in memory even quantized down…
I run a little pipeline that builds history-explainer videos end to end — script, narration, images, video — all automatically, all by myself. Up until one day, the background was a single picture, s…
My project's docs had rules. "One document, one responsibility." "Split anything over 45 lines." I wrote that. The day before yesterday. Here's how that was going. - Folders with no README (no index)…
One morning, an email landed. Subject line: 'your cloud cost reduction setup?' That one lands cleanly, honestly. Cloud cost reduction is one of the things I put on my public shingle, so the sender ju…
I'll confess up front: this is basically a sequel to my earlier piece, the one where an AI decided it was being hacked when nobody was attacking it, and spiraled. An AI lied to me again. Only this ti…
There's a small corporate site. A few days after launch, one piece of spam landed in the contact form. Zero actual damage. Just a lazy ad. But there were two real problems. One: no spam protection at…
Same old story: I'm running the SaaS our CFO shipped to production in two days. A non-engineer exec builds something fast with Claude Code, and the engineer (me) goes through the back end one piece a…
One evening, a monitoring alert went off: a server behind a web service was down. I handed the incident to Claude Code. Half experiment, half laziness — "it's routine triage, what could go wrong." Le…
Let me confess something a little creepy. I have a habit of peeking at other people's dev posts. Not stealing the writing — relax. I run a tiny read-only job that fetches the public pages on dev.to,…
There's a B2B SaaS that a non-engineer executive built all the way to production in two days , by handing everything to an AI. Real customers use it. It works. Features ship fast. It's genuinely impr…
One morning, a bunch of EC shops sharing a single server all tripped their monitors at once with "response timeout." Let me be honest up front: the outage itself self-recovered in about five minutes.…
This is the story of how a mundane complaint — "the VPN is slow" — turned into a US patent application. Not a granted patent. An application . I want to be precise about that from the start, because…
Introduction Dynamic Programming is an efficient algorithm design technique used to solve problems by breaking them down into smaller subproblems. It stores the results of these subproblems to avoid…
Problem Given a list of weights and values and a total capacity, determine the maximum value that can be placed in the knapsack. 2D DP 1D DP (space optimized)
Problem Given two strings, find the length of their longest common subsequence. Tabulation Approach (2D DP)
Problem Given an integer array, return the length of the longest strictly increasing subsequence. Tabulation (O(n^2))
Introduction Dynamic Programming is an efficient algorithm design technique used to solve problems by breaking them down into smaller subproblems. It stores the results of these subproblems to avoid…
Introduction Segment Tree is an efficient tree data structure for dynamic range queries. This is why it is called a "Segment Tree." The array is recursively divided into two segments until the segmen…
The following Python code finds perfect numbers within a given range: Running this code will output perfect numbers such as 6, 28, 496, and 8128. --- Efficient Perfect Number Checking Using Mersenne…
Versions Homebrew 3.4.7 Nginx 1.21.6 Ngrok 3.0.2 AWS CLI 2.5.8 About AWS ECR AWS ECR is a repository service like DockerHub. You can create your own repository, either public or private. How to 1. Pr…
Versions Homebrew 3.4.7 Nginx 1.21.6 Ngrok 3.0.2 About Ngrok - A tool that makes the specific port of local machine public on internet - Pricing: Free for personal use - Official website: https://ngr…
URL: https://leetcode.com/problems/longest-substring-without-repeating-characters Difficulty: Medium Problem Statement Given a string, find the length of the longest substring without repeating chara…
We can declare variables with let. let binds variables. Binding is the process of associating a variable name with a value. Variables can refer to the value bound to them. If the value bound to the v…
Let's implement an efficient function to compute the greatest common divisor using recursion in Python. The original code is borrowed from Algorithm Science: A Beginner's Guide by Tetsuo Asano, P.73.…
Let's implement an efficient power function using recursion in Python. The original code is borrowed from Algorithm Science: A Beginner's Guide by Tetsuo Asano, P.70. --- Full Code You can compute th…
https://leetcode.com/problems/divide-two-integers Difficulty: Medium In this article, I will explain how to solve the problem Divide Two Integers with Timothy H Chang's solution. His solution is best…
https://leetcode.com/problems/remove-duplicates-from-sorted-array Difficulty: Easy This is easy problem. Just remove duplicates from array. And the array is sorted. I will explain my code. ※ You need…
https://leetcode.com/problems/maximum-number-of-vowels-in-a-substring-of-given-length Reference Code: [[Java/Python 3] Slide Window O(n) codes](https://leetcode.com/problems/maximum-number-of-vowels-…
https://leetcode.com/problems/length-of-last-word Very easy problem. You can try out your new programming language here. Problem Given a string s consisting of words and spaces, return the length of…
Prepare Docker Image at ECR If you don't have an image at ECR, please check this article and get it. Push Docker image to AWS ECR In this article, I use React app image. About ECS AWS Elastic Contain…
Context Context in React.js provides a way to pass data through the components without props. We can avoid to pass props again and again. (Parent to child via props) useContext Code below shows "Jun…
Effects We can perform data fetching, subscribing, and manually changing DOM from React components. In React, we call these operation 'side-effects' or 'effects' in short. And we have to use useEffec…
State In React, state is a data that is stored in the component. It is used to store data that changes over time. For example, if you want to store the number of times a button is clicked, you can us…
Binary search is an algorithm to check if a target number exists in a list. The time complexity of this algorithm is O(log N). Prerequisites - The list elements must be numbers. - The list must be so…
URL: https://leetcode.com/problems/132-pattern Difficulty: Medium Even though the tag of this problem is "Binary Search", you can solve this problem without using binary search. However, it is a prob…
URL: https://leetcode.com/problems/intersection-of-two-arrays Difficulty: Easy This is a simple and easy problem. Although, I solved this problem using binary search, and a funciton that remove dupli…
https://leetcode.com/problems/sqrtx My answer was O(n), so the execution time was too long. To reduce the time complexity to O(logn), I will explain the solution using binary search. I aim to improve…
Versions Node version: 16.13.0 Docker version: 20.10.12 Link GitHub Repo https://github.com/jun-uen0/react-dockerfile Here’s How to Dockerize React App https://www.bacancytechnology.com/blog/dockeriz…
Versions OS: MacOS (intel chip) Docker version: 20.10.12 Official image of Nginx Nginx distribute its official Docker image on Docker Hub. https://hub.docker.com/ /nginx How to 1. Pull Nginx Docker i…