About me
Learn more about me
I am René Gerritsena developer
I enjoy writing code – both professionally and privately. I mostly work in the backend, with APIs, automation, or directly on the CPU, e.g. in 6502 assembler.
Technologies such as Go, Python, PHP, JavaScript, Docker, and Git are part of my everyday life. I'm interested in robust architectures, testing, CI/CD, and anything that helps keep systems understandable and maintainable.
In my free time, I spend a lot of time on retro computing. I restore old Macs and write software for classic systems like the Macintosh SE/30. I'm especially proud that my SE/30 became part of an exhibition.
My interests range from clean code, OWASP, and alternative development environments such as NixOS to topics such as 3D printing, gaming, and NES programming in assembler.
- Name:René Gerritsen
- Email:rene.gerritsen@me.com
- Place of residence:Heek, Germany
20 Years
Experience as a developer
7+
Programming languages
100%
Passion for Docker & Cloud
∞
Interest in technology
Writings
Blog
Gitlab Virtualbox Runner
02.02.24Völliger automatisiertes einrichten eines Ubuntu Maschine als Gitlab VM Runner
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Filter, Paginate, Sort in new Backend Architecture
28.05.25Analyse und Vergleich verschiedener Ansätze zur Filterung, Sortierung und Paginierung in einer neuen Go-basierten Backend-Architektur.
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Services
What I Do?
Custom software development
Development of APIs, plugins, and tools in PHP, JavaScript, and Go.
E-commerce platforms
Working with Shopware and Magento – customization, integration, expansion.
Travel industry
APIs and integrations in the hotel and vacation rental sector.
Legacy code
Refactoring and gradual modernization of existing applications.
CI/CD pipelines
Setups with containers, automated tests, and deployment processes.
Technical consulting
Assessment of code, architecture, and development processes.
CV
Curriculum vitae
Experience
2022 – Present
Senior Software Developer
NFON AG – Cloud Telephony, Munich
Working in an English-speaking, international team. Further development and maintenance of the central ‘Cloudya’ API for web and mobile applications. Migration to Golang and PHP 8, introduction of automated testing. Setting up Docker-based development environments and CI/CD pipelines with Bamboo. Integration of external interfaces. Error analysis and security optimization.
2016 – 2022
Professional Software Developer
Check24 Hotel – Comparison portal, Munich
Real-time search with live queries for the best offers. Development of backend APIs, refactoring of legacy code, introduction of database migrations and software testing. Integration of hotel providers and channel managers. Development of cluster matching for over a million data records from multiple providers, including search and booking logic. Focus on scalability, performance and robust integrations with SQL, PHP and JavaScript.
2009 – 2012
Software Developer
Wildcat Deutschland GmbH – Piercing Großhandel, Gronau
Development of a RIA with 3D preview for jewelry customization, including API connection to production and billing. Setup and maintenance of a B2B shop. Shopware plugin development. Web-based iPad apps. Maintenance of several brand shops.
My skills
Web development
PHP Development 90%
JavaScript 85%
Golang 70%
Bash 70%
SQL 85%
API Development 85%
Shopware Development 75%
Magento Development 70%
Full Stack Development 80%
React / ExtJs / HTML / CSS 75%
DevOps and testing
Docker 90%
CI/CD & Container 90%
Unit and Functional Testing 90%
Software Fundamentals
Problem Solving 90%
Refactoring 85%
Clean Code 85%
Software Pattern 80%
Software Architecture 85%
AI / ML
LangChain / LangFlow 60%
Python 70%
Sympy / Numpy 65%
Tensorflow / Neural Networks 40%
3D & Design
Blender 60%
Photoshop 10%
My Work
Links
Testimonial
Client Speak
Dr. Jochen Bielek Head of Backend - Check24
“Mr. Gerritsen possesses extensive and versatile expertise, which he always applies confidently and purposefully in practice.”
Carolin Stutzmann Head of Staff - Wildcat
“Mr. Gerritsen worked for us on a project basis and was hired full-time as of October 1, 2010.”