Stefan Hagemann

● Orchestrated the migration of a legacy Laravel monolith to a scalable microservices ecosystem using the Strangler pattern, rewriting core services in Node.js and Python frameworks (NestJS, FastAPI) behind AWS API Gateway, implementing Saga based distributed transaction management. ● Developed modular backend features such as API rate limiting, pagination, and custom error handling middleware in FastAPI, ensuring robustness and scalability under increasing request loads. ● Designed and implemented asynchronous background task queues using Celery with Redis and RabbitMQ to handle notifications, document processing, and external service integrations. ● Integrated AI-powered features into internal tools using LangChain, orchestrating LLM workflows for document parsing, semantic search, and contextual chatbots that reduced manual support requests. ● Built LLM-driven microservices on FastAPI with OpenAI APIs and vector search, delivering real-time semantic insights across shipment and routing data. ● Modernized frontend infrastructure using Next.js, TypeScript, Tan-Stack Query, Redux Toolkit, and Tailwind CSS, with Storybook for isolated component development and SSR, SSG, and ISR for optimal performance and SEO. ● Developed cross-platform mobile apps in React Native with TypeScript, implementing biometric authentication (Touch ID / Face ID) and push notifications for iOS and Android. ● Implemented CI/CD pipelines with GitHub Actions, Docker and AWS CodePipeline to automate build, test, and deployment processes, enabling zero downtime releases and reducing release lead time by 50%. ● Configured pre-commit hooks using black, flake8, and isort to enforce Python code formatting, linting, and import order, integrated SonarCloud with CI/CD pipelines to maintain quality gates and catch potential issues early.

● Designed and delivered a healthcare billing and claims management module supporting automated billing, claim submission, eligibility verification, and payment posting for healthcare providers, using Node.js, Python, and React. ● Integrated HL7 v2 and FHIR UK Core APIs with Mirth Connect and custom Python adapters to enable real-time, GDPR-compliant data exchange between Electronic Health Records (EHR), payers, and NHS Digital services. ● Architected and deployed scalable serverless platforms for SaaS-based B2B and B2C applications using AWS Lambda, API Gateway, AWS AppSync, and DynamoDB, integrating AWS IAM for secure access control, while ensuring high availability and seamless auto-scaling. ● Designed and managed scalable infrastructure with AWS CDK and CloudFormation, streamlining deployments faster and more reliable across different environments. ● Optimised system performance and cost efficiency by reducing cold start latency, implementing asynchronous workflows with SQS & SNS, and introducing caching strategies with Redis and DynamoDB Accelerator (DAX). ● Demonstrated strong problem-solving, communication, and collaboration skills, effectively working with cross-functional teams to deliver scalable solutions, streamline workflows, and drive project success in fast-paced environments.

● Architected and built a digital products delivery platform using Python (Django), React, and MongoDB within an open-source ecosystem, enabling dynamic product catalogs and real-time inventory management. ● Developed scalable RESTful and GraphQL APIs in Node.js (Express) and Python (Flask), handling 100K+ daily requests with sub 200ms average response times and robust error handling. ● Integrated Stripe and PayPal payment gateways with automated invoicing and refund workflows, achieving a 99.8% transaction success rate and reducing manual payment support by 35%. ● Designed a secure digital asset delivery pipeline on AWS S3 and CloudFront with expiring signed URLs, ensuring instant, reliable downloads and preventing unauthorized access. ● Developed a Python-based license key generation and management microservice with RESTful APIs and AWS SES notifications for renewals, cutting support ticket volume by 45%. ● Optimized search and analytics capabilities by integrating Elasticsearch with MongoDB, implementing efficient indexing, query tuning, and real-time data synchronization for faster and more accurate search results. ● Spearheaded frontend performance optimization using Webpack and React - implementing code splitting, lazy loading, tree shaking, and critical CSS to cut page load times by 40% and achieve 90+ Lighthouse scores. ● Established TDD/BDD workflows with Jest, Pytest, and Cucumber, integrating tests into GitHub Actions and Jenkins pipelines to maintain 80%+ coverage and reduce production defects by 60%. ● Collaborated with DevOps to containerize services in Docker and orchestrate deployments on AWS ECS/EKS, automating rollouts and rollbacks to cut provisioning time by 70% and boost uptime.