Holger Just
Software Engineer at Planio
Berlin, Germany
Summary
🤩
RockstarHolger Just is a seasoned software engineer based in Berlin with 16 years of experience building and hardening backend systems and developer tooling. He currently contributes at Planio and is an active open-source maintainer in the Ruby/Rails ecosystem, improving libraries like concurrent-ruby and lograge to make concurrency safer and Rails logging more practical for production. Holger blends hands‑on QA discipline with backend engineering—adding tests, fixing edge-case bugs, and clarifying platform-specific behavior such as JRuby processor counts. A pragmatic DevOps advocate, he focuses on maintainability and observable systems rather than flashy frameworks. He’s driven by curiosity—“pressing buttons to change patterns of lights”—and has a track record of quietly improving developer experience and resilience in widely used projects.
16 years of coding experience
Stackoverflow
54,244reputation
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909answers
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Github Skills (57)
ruby-rails10
debug10
rubygems10
testing10
rspec10
rails10
ruby10
activerecord10
chef-infra10
logging10
unit-test10
ruby-on-rails10
concurrency10
mysql9
githubactions9
Programming languages (11)
Github contributions (5)
chiliproject/chiliproject
Feb 2011 - Feb 2015
ChiliProject is a web based project management system built on Ruby on Rails
Role in this project:
Back-end Developer & QA Engineer
Back-end Developer & QA EngineerContributions:339 commits, 181 PRs, 1 push in 4 years
Contributions summary:Holger's contributions focused on enhancing the query functionality and associated testing within the ChiliProject project management system. They addressed issues related to handling empty sets in query value lists, adding unit tests to ensure proper behavior with empty sets, and fixing bugs within the core query model. These changes aimed to improve the robustness and reliability of the query feature, crucial for issue tracking and reporting within the application. Further contributions included a merge related to handling RubyGems 1.6 deprecation.
ruby-on-railsmanagement-systemproject-management-systemrailsweb-based
ruby-concurrency/concurrent-ruby
Feb 2017 - Dec 2022
Modern concurrency tools including agents, futures, promises, thread pools, supervisors, and more. Inspired by Erlang, Clojure, Scala, Go, Java, JavaScript, and classic concurrency patterns.
Role in this project:Backend Developer
Backend DeveloperContributions:6 commits, 7 PRs, 5 comments in 5 years 11 months
Contributions summary:Holger focused on improving the quality and maintainability of the `concurrent-ruby` library. Their contributions include fixing code comments and correcting potential issues arising from array slicing on Rubinius. Furthermore, they initialized thread-local variables and addressed warnings in the spec files, ensuring code correctness and preventing unexpected behavior. They also updated the documentation for `processor_count` on JRuby, clarifying its behavior.
supervisorsthreadpatternserlangconcurrent-programming
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