Hybrid Senior Backend Engineer – Kotlin, Spring Boot

at E.ON

• Job title: Senior Backend Engineer – Kotlin, Spring Boot
• Job type: Full Time
• Experience level: Senior
• Salary: Not specified
• Degree requirement: No Education Requirement
• Tech skills: AWS, Cloud, GraphQL, Kotlin, Spring, Spring Boot, SpringBoot
• Location requirements: Hybrid, Koln, Germany

About the role

• Senior Backend Engineer developing Kotlin backend services for E WIE EINFACH in Köln. Responsible for cloud-native architectures and API-driven integrations on AWS.

Responsibilities

• Develop small, focused backend services in Kotlin and Spring Boot using cloud-native technologies for integrations and custom business logic
• Design and implement event-driven architectures on AWS
• Design, specify and implement APIs (REST and GraphQL), including versioning, documentation (e.g., OpenAPI), and authentication/authorization concepts (e.g., OAuth2, JWT)
• Review and enforce provider-side API contracts to ensure backward compatibility and secure API evolution
• Integrate third-party services such as payments, credit checks, notifications, or document workflows
• Take end-to-end responsibility for backend delivery: development, deployment and production readiness
• Implement and maintain Infrastructure as Code and CI/CD pipelines for your services in GitLab
• Ensure security, reliability and observability are considered throughout the design
• Work closely with Architecture, Operations and QA in Agile/Scrum teams
• Use AI agents for autonomous code generation and focus on strategic reviewing, architecture and efficient human-in-the-loop processes

Requirements

• Several years of experience as a Backend Engineer, ideally with cloud-native architectures on AWS
• Strong knowledge of Kotlin / Spring Boot and experience building API-driven integrations
• AI-native developer mindset: proficient with agent-driven workflows using tools like Claude Code, Cursor (Composer) or Windsurf (Cascade)
• Practical experience with DevOps fundamentals: CI/CD, Infrastructure as Code, cloud deployments
• Solid understanding of API-first systems (REST/GraphQL) and asynchronous integrations
• Strong ownership mentality and ability to collaborate across teams
• Confident communication in German and English

Benefits

• A highly motivated team with flat hierarchies and short communication paths
• An office in the heart of Cologne and the option for hybrid work
• Lots of fun at work and within the team
• Competitive pay and 30 days of vacation per year
• Subsidized job ticket and free parking spaces