References

Founder, Architect & Lead Developer · Own product (JNK Consulting)

Design, development and operation of an online ordering platform for restaurants – from the customer shop and restaurant back office to POS and receipt printer integration. Self-hosted infrastructure instead of SaaS.

• Microservice architecture (order, admin, flow, Stargate integration hub) with Spring Boot, REST and RabbitMQ
• Customer shop and admin UI in Angular; Android and iOS apps for restaurants including receipt printing
• Identity with Keycloak (customer and restaurant realms), payments with Stripe Connect
• Infrastructure on Hetzner Cloud with Ansible, Traefik and Docker; GitLab CI/CD through to deployment
• Observability stack with Grafana, Loki, Tempo, Prometheus and OpenTelemetry including alerting
• Nationwide address/geocoding index built on OpenStreetMap data, including load testing
• AI-assisted development throughout with Claude Code (spec → plan → subagents → review)

• Kotlin
• Java
• Spring Boot
• Angular
• RabbitMQ
• MariaDB
• Keycloak
• Stripe
• Docker
• Ansible
• GitLab CI
• Grafana

Senior Engineer & Tech Lead AI-Assisted Development · Software vendor for digital signature workflows · 5 days/week; 10/2023 – 09/2024 2.5 days/week · Team: 6–8 people

Continued development of a platform for document-centric workflows and digital PDF signing, along with the introduction of AI-assisted, agentic software development in the team.

• Introduced agentic development with Claude Code for a growing team (currently 5 developers)
• Workshops on using AI agents effectively – proven practices and common pitfalls
• Guardrails and a secure working environment for agents – including shielding credentials and secrets from agent access
• Continued development of the platform in backend and frontend, including integration of an identity service
• Extended authentication with OAuth2
• Multi-inbox – parallel document workflows for external users
• Maintenance of the Android apps, framework upgrades, backward-compatible API updates

• Claude Code
• Java
• Kotlin
• Angular
• Spring
• Hibernate
• MariaDB
• Oracle
• MS SQL
• DB2
• Jenkins

Backend Developer & Architect · Software vendor for digital signature workflows · Team: 3 people

Spring Boot microservice in Kotlin that requests identities from external identity providers, manages them and provides them for electronic document signatures.

• Architecture, code structure and communication protocol of the microservices involved
• OpenAPI-based API design between frontend, backend and the identity provider
• Implementation of the Kotlin backend including the persistence layer
• CI/CD pipeline, automated deployment to multiple stages and monitoring integration

• Kotlin
• Spring Boot
• OAuth2
• JPA
• MariaDB
• Docker
• GitLab CI
• Grafana
• Kibana

Full-Stack Developer · Optical retail chain · 4 days/week; from 10/2023 2.5 days/week · Team: 7 people

Continued development of a retail chain's online appointment system: minimal waiting times in the stores and optimised staff scheduling.

• Migrated a self-hosted Kubernetes cluster to AWS EKS
• Replaced Concourse CI with GitHub Actions; faster, more reliable deployments
• Migrated monitoring from Grafana to Datadog
• New features in backend and frontend, integration of external systems

• Kotlin
• Next.js
• Spring Boot
• GraphQL
• PostgreSQL
• AWS
• Kubernetes
• Kafka
• GitHub Actions
• Datadog

Java Developer · Software vendor for digital signature workflows · alongside employment until 06/2021, 07–09/2021 5 days/week, from 10/2021 1 day/week · Team: 6–8 people

Continued development and maintenance of a digital signature platform in Java/GWT.

• Bug fixing, framework upgrades and customer-specific adaptations

• Java
• GWT
• Spring
• Hibernate
• Jersey
• Jenkins

Java Developer & Solution Design · IT service provider in insurance

Replaced an EJB service with a REST service for accessing a compliance-grade document archive in the insurance sector, plus a Spring-based caching library for REST calls.

• Migration and implementation concept, full implementation as a Spring Boot service
• Design and implementation of the caching library including a performance estimate
• Documented release packages

• Java
• Spring Boot
• Resilience4J
• Redis
• Maven