Senior Backend Developer | Problem Solver for Legacy → Scalable Systems | Node.js · Python · Next.js
Munich, Deutschland
Nur Remote
Bachelor of Science (BSc) Applied Computer Science with a Focus on Media Informatics
Munich, Deutschland
Nur Remote
Bachelor of Science (BSc) Applied Computer Science with a Focus on Media Informatics
Profilanlagen
Resume Frank-Dieter Stadtler.pdf
Über mich
The engineer teams call when a backend has grown past what its original design can hold. Ten years in, mostly Node and Python, working remotely on EU hours. I like the messy projects — legacy migrations, broken integrations, debugging that takes patience.
Senior Backend Developer specializing in Node.js/NestJS, Python/Django, and PostgreSQL. I help companies fix production issues, eliminate technical debt, and scale API infrastructure that's hitting its limits.
What I Do Best
Backend & API Systems: Production-grade REST and GraphQL APIs, architecture redesign for systems under strain, database optimization (PostgreSQL, MySQL, MongoDB, Redis).
Emergency Problem-Solving: Diagnosing and resolving critical backend failures — the kind where something broke in production and the team can't figure out why. Calm under pressure, fast to root cause.
Technical Debt & Legacy Code: Turning fragile, undocumented systems into stable, maintainable platforms. Modernizing codebases without breaking what works.
Cloud & Infrastructure: AWS, Google Cloud, Docker, CI/CD pipelines, Terraform. Practical DevOps for teams that need reliable deployments, not theoretical perfection.
How I Work
I take ownership of complex technical problems and deliver clarity — not just code, but understanding of what was wrong, what was fixed, and what to watch for next. Experienced working with small teams and startups where one person needs to cover a lot of ground.
Project-based engagements through EU company (Bulgarian EooD, VAT-registered). Typical engagements: 2–12 weeks for defined projects, or ongoing retainer for teams that need reliable backend expertise on call.
Stack
Languages:
Python
TypeScript
JavaScript
Frameworks:
Node.js
NestJS
ExpressJS
Django
FastAPI
Databases:
PostgreSQL
MySQL
MongoDB
Redis
Infrastructure:
AWS,
Google Cloud
Docker
Terraform
CI/CD
Capacity for concurrent engagements: 20–40h/week depending on project scope. Available for DACH and international clients. 100% remote with guaranteed CET morning overlap and partial US working hours for seamless collaboration. On-site only considered for workshops or kickoffs on larger project budgets (100k EUR+).
Erfahrung
Berufserfahrung5 - 10 Jahre
Freelancer seit2016
Sprachen
DeutschMutterspracheEnglischverhandlungssicher
Projekthistorie
Backend Developer
QUANTUM Int. GmbH & Co. KG (Client WiWin GmbH)
Internet und Informationstechnologie
10-50 Mitarbeiter
Project Summary
Backend developer responsible for the Partner API of WiWin, a German crowdinvesting platform for sustainable projects that tokenizes equity investments using blockchain technology. Designed and built a configurable Partner API that lets partner companies create and manage users and investment flows, integrating the platform's internal GraphQL layer with external REST interfaces.
Tasks & Responsibilities
Designed and implemented the Partner API from scratch with NestJS, bridging internal GraphQL and external REST interfaces; in production handling 500K+ requests/day at ~99.99% availability
Restructured the KYC process; implemented idempotent endpoints, role-based access control (RBAC) and partner-originated user flows
Optimized data structures and SQL access for high throughput; wrote unit tests and integrated the Partner API into the existing CI/CD pipelines
Extended the existing AWS CloudFormation setup with a new part for hosting the Partner API (ECS, RDS/PostgreSQL) and adjusted Lambda functions already running in production
Reviewed 100+ merge requests, focusing on maintainability, performance and security
Set up customer activity tracking with Google Analytics to support data-driven product decisions
Established documentation practices that made onboarding easier for new developers
Rebuilt the hotel SaaS DailyPass as a new platform under the UpGuest brand: replicated the existing system, set it up as a separate project with refreshed branding, and extended it with new booking and check-in features for hotels.
Tasks & Responsibilities
Replicated and rebranded the DailyPass platform as UpGuest, including backend, frontend and deployment
Implemented timeslot booking to extend the voucher/product offering, e.g. bookable cooking classes
Added capacity management for high-demand services such as hotel breakfast buffets
Built document data extraction into the online check-in: extracted ID data, booking details and a copy of the document are stored together per check-in
Optimized the booking and check-in flows for mobile devices
Replaced Google Maps API integrations with iFrame embeds
Fullstack development with Python/Django and React (TypeScript); CI/CD with Docker on Google Cloud
Fullstack developer on DailyPass, a SaaS platform that lets hotels sell day-use amenities such as pool access or one-day gym passes. Worked directly with the CTO on requirements and architecture and coordinated feature development across the developer team.
Tasks & Responsibilities
Evaluated the Saleor e-commerce framework (Python/Django, GraphQL API, React storefront and admin) and extended it for hospitality-specific use cases
Designed and implemented fullstack features for selling hotel amenities, from data model and API to storefront
Backend services with GraphQL, PostgreSQL and Redis; CI/CD with Docker on Google Cloud
Translated business requirements into Jira tickets, specifications and documentation
Delegated tasks across the developer team, supported developers and did code reviews
Tracked and reported project progress to CTO, CEO and CFO
Senior Fullstack Developer / Principal Engineer / Solutions Architect
Mashub Pte Ltd
Internet und Informationstechnologie
< 10 Mitarbeiter
Project Summary
Led cross-functional initiatives that combined project management, developer coordination, and hands-on engineering to accelerate delivery timelines, optimize resource allocation, and improve system performance. Balanced leadership and technical execution to ensure high-quality outcomes across multiple projects, including a trading prototype for Robinhood. Tasks & Responsibilities
Translated complex business requirements into actionable Jira tasks for a 10-developer cross-functional team — reducing project delivery time by 40% through greater clarity and efficiency.
Strategically matched freelance developers to tasks based on their skill sets, optimizing resource allocation and boosting task completion rates by 30% while maintaining high code quality.
Conducted rigorous testing and debugging across multiple projects, identifying critical errors that improved overall system performance by 25%.
Collaborated with engineers to prototype an Order Routing System for Robinhood, capable of processing up to 5,000 orders per hour with reliability and efficiency.
Fullstack developer for Travel Ads Network across several travel products, including the hotel booking marketplace Deetrip. Selected work: the core booking engine and the Node.js services connecting it to TripAdvisor, including a rule-based engine for tax and fee calculation.
Tasks & Responsibilities
Extended the accommodation booking engine (PHP/CodeIgniter, Python 3, vanilla JavaScript)
Built a TripAdvisor service for batch querying the booking engine (Node.js, LoopBack 3, Redis)
Designed a rule-based tax service that reverse-calculates net price, taxes and fees from gross prices to meet TripAdvisor's display requirements; covers Thai tax rules where specific rules override general ones
Rules defined as JSON configuration and loaded at API start; heavy caching of rule evaluation and results to sustain 200 requests/second
Worked with the data scientist to turn prototypes into production APIs (Python, Flask, Redis, Pandas)
Set up infrastructure on Google Cloud (GCE, load balancer, firewall)
Freelance fullstack development for own SaaS products and client projects. Main project: a microservice-based SaaS around Instagram, built with a business partner, including Angular dashboards for operators and a platform connector that was re-architected several times as the platform changed its interfaces.
Tasks & Responsibilities
Instagram SaaS: Angular dashboards where operators select from pre-filled content for profiles, set up new accounts and analyse followers
Node.js microservices with worker and queue-based processing
Re-architected the system several times in response to platform interface changes, including a browser-automation-based version on dedicated hardware
Extracted the platform integration into a standalone, replaceable connector service (PHP, later Python), keeping the core system unchanged
Questionnaire backend for international competency evaluations, including EU funding logic
Contract and document management system for easier tracking and retrieval
Software developer at ROD Medias, building automation and data tools for KLIM Technologies, an Amazon FBA e-commerce company for gaming peripherals. Built Angular/Node.js web applications for keyword research and logistics, plus integrations and automations for internal processes.
Tasks & Responsibilities
Keyword and channel research tool based on YouTube API data (Angular, TypeScript, Node.js, LoopBack, RabbitMQ, MySQL)
Logistics module with just-in-time order notifications and API-based order quantity recommendations to avoid stockouts and excess FBA storage (Angular, TypeScript, Node.js, LoopBack, RabbitMQ, MySQL, Docker)
Chrome extension that interacts with and parses a live website to automate repetitive manual steps (JavaScript, Ajax)
Custom integration between a job queue and Slack (Node.js, LoopBack, RabbitMQ, REST)
Data transformation from Amazon reports to the Xero accounting system (Google Sheets API, JavaScript)
Zapier automations for the hiring process and task assignment; multilanguage extension of a WordPress plugin (PHP)
Tech Stack
Angular · TypeScript · Node.js · LoopBack · RabbitMQ · MySQL · Docker · JavaScript · Google Sheets API · Zapier · WordPress/PHP
Customer Service
KLIM Technologies
Konsumgüter und Handel
10-50 Mitarbeiter
Project Summary
Customer service for KLIM Technologies, an Amazon FBA e-commerce company for gaming peripherals and electronics. Handled customer support, replacements and reviews, and translated product documentation, which led directly into automation and tooling work for KLIM through ROD Medias.
Tasks & Responsibilities
Answered customer inquiries and handled technical support questions
Processed replacements and complaints
Monitored and responded to reviews and customer feedback
Translated user manuals and marketing material
Tech Stack
Amazon Seller Central · Customer Support · Technical Translation
Software Developer
CDA GmbH
Industrie und Maschinenbau
50-250 Mitarbeiter
Project Summary
Software developer at CDA GmbH, a German technology company for micro-optics and precision components serving automotive, industrial and consumer electronics customers. Worked on production traceability and the ERP migration from SAP to Dynamics NAV.
Tasks & Responsibilities
Traceability from raw plastic granulate to shipping for an automotive customer; the external software had no documentation and no reachable developers
Applied software archaeology: code analysis, reverse engineering of the database structure, and walking the process machine by machine with the head of production and mechanics
Documented the as-is system and designed a modular target architecture incl. ER model, turning the hard-coded workflow into configurable steps where machines can be added, removed and reordered; also the topic of my bachelor thesis
ERP migration: learned the SAP data structures with colleagues, the SAP provider and the implementation agency; after C/SIDE certification implemented Dynamics NAV customizations independently, reviewed by the agency developer
Long-term archiving for 15–20 year automotive retention: C#/.NET tray application wrapping a proven CLI tool for recovery data, with scheduling, saved settings and configurable redundancy
Tech Stack
Microsoft Dynamics NAV (C/SIDE) · C#/.NET · SAP · MS SQL Server · ER Modeling
Software Developer
Kartosoft GmbH
Internet und Informationstechnologie
< 10 Mitarbeiter
Project Summary
Delivered a custom Time Recording Module for a niche ERP platform in the paper processing industry. The engagement required rapid onboarding into a VB6-based system with an MS SQL Server backend, analyzing production workflows, and implementing a reliable solution under strict deadlines.
Tasks & Responsibilities
Analyzed the existing VB6 ERP architecture to determine integration points for the new module.
Designed and implemented a Time Recording Module supporting industry-specific production processes.
Conducted testing to ensure seamless integration with existing ERP workflows and database consistency.
Produced technical documentation to assist the internal team with maintenance and further extensions.
Tech Stack
VB6 · Microsoft SQL Server · Custom ERP Platform
ERP Systems Developer & IT Solutions Specialist
ACO Passavant GmbH
Architektur und Bauwesen
250-500 Mitarbeiter
Project Summary
Contributed to the optimization of internal operations at a mid-sized manufacturing company by customizing the proALPHA ERP system and building supporting tools for production, HR, and executive management. Delivered reliable solutions that improved reporting, tracking, and data management across departments.
Tasks & Responsibilities
ERP Customization: Developed reports, custom data entry masks, and workflows in proALPHA ERP, streamlining daily operations.
Production Tools: Built an Excel/VBA-based production tracking system and a failure rate analysis tool, enabling better visibility into manufacturing efficiency.
HR Tools: Designed and deployed a PHP/JavaScript/MySQL platform for business trip requests, replacing manual processes.
Executive Tools: Engineered a C++/Qt backup utility for executive laptops, with MD5-based file-change detection and VPN sync (automated rsync).
Inventory System: Implemented a hybrid MS Access + REST API + SQL solution for inventory management, including a sync algorithm to unify naming conventions and prevent duplication.
Tech Stack
proALPHA ERP · SQL · Excel/VBA · PHP · JavaScript · MySQL · C++/Qt · MS Access · REST APIs
Zertifikate
SQL Server 2012
Microsoft
2014
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