A Java geek

Making illegal state unrepresentable

A couple of years ago, I wrote that The Builder pattern is a finite state machine!. A state machine consists of states and transitions between them. As a developer, I want to make illegal states unrepresentable, i.e., users of my API can’t create non-existent transitions. My hypothesis is that only a static typing system allows this at compile-time. Dynamic typing systems rely on runtime validation. In this blog post, I will show that it holds true, with a caveat.

Technical

A GitHub agentic workflow

Last month, I became aware of GitHub agentic workflows. I read the site carefully, but the use cases weren’t very exciting to me. I tried the continuous documentation It didn’t work out initially, and because of my lack of involvement, I left it as it was. However, I succeeded in another one that I want to describe in this post. With lessons learned here, I managed to make the documentation workflow work!

Technical

Experimenting with AI subagents

I like to analyze codebases I start working on, or that I left for months. I ask my coding assistant, case in point, Copilot CLI: 'analyze the following codebase and report to me improvements and possible bugs.' It’s vague enough to leave room for crappy feedback, but also for some interesting insights. I did it last week on a code base. Copilot returned a list of a dozen items. I asked it to create a GitHub issue for each, with the relevant labels, including priority.

Technical

One tip for successful OpenTelemetry projects

Leading your organization to use OpenTelemetry is a challenge. In addition to all the usual project hurdles, you’ll face one of these two situations: convince your teams to use OpenTelemetry, or convince them to move from the telemetry tool they are already using to OpenTelemetry. Most people don’t want to change. You’ll need lots of effort and baby steps. My tip is the following: the fewer the changes, the higher your chances of success.

Book

The Software Architect Elevator

I don’t think it’s necessary to introduce Gregor Hohpe. I’m a big fan, having read Enterprise Integration Patterns, and I’ve recommended the book ever since. When I spoke at the Software Architecture Gathering in 2024, I was fortunate enough to meet him and purchase this book. I’m the happy owner of a signed copy. Modern architects don’t try to be the smartest people in the room–they make everyone else smarter.

Technical

Writing an agent skill

Most developers now use coding assistants. I do too—Copilot at work, Claude Code at home. As a developer, I prefer not to repeat myself. This post explains why and how to avoid repetition as a skill. Don’t Repeat Yourself The DRY principle has been present in the software development field for ages. The idea is that if you copy and paste code in multiple places and a bug appears, you’ll need to fix the bug in all these places.

Technical

Pi-hole behind Tailscale

As I age, I become increasingly cautious about my privacy. The slope the world is sliding on is also a big, unfortunate incentive. I have been eying Pi-hole for some time: in this post, I want to explain what it does, how to install it on a Raspberry Pi, and how to integrate it with Tailscale. My take on privacy Privacy, or more specifically digital privacy, is the ability to protect oneself from the constant data collection by legitimate companies and malicious actors alike when online.

Technical

Ready-to-use virtual clusters

vCluster is a solution for creating virtual clusters within a host Kubernetes cluster. Virtual clusters are a Kubernetes concept that enables isolated clusters to be run within a single physical Kubernetes cluster. Each cluster has its own API server, which makes them better isolated than namespaces and more affordable than separate Kubernetes clusters. — What are virtual clusters?

Java

JVM timing options

For as long as I have been coding in Java, we have had requirements to measure the execution time of blocks of code. While the current good practice is to use OpenTelemetry’s traces, not every company has reached this stage yet. Plus, some of the alternatives are OpenTelemetry-compatible. Let’s see them in order. The basic option The basic option is what we have been doing for ages, and what the other options rely on anyway. It’s based on the following API: System.

A Java geek

Nicolas Fränkel's blog