Senior) Backend Engineer in Green-Tech Startup; m​/f​/d

About the role

KUGU makes buildings CO‑2‑neutral and actively shapes the energy transition. From small co‑operatives to large housing companies, demand control, system maintenance, and consumption monitoring are daily challenges that are still characterised by manual processes.

The solution is digital data collection, intelligent analysis and automated solutions to increase efficiency and reduce energy consumption. Our decarbonisation platform supports the housing industry with innovative products to achieve their emission targets cost‑effectively.

You will join a cross‑functional backend team building and evolving the core platform services. You will design and implement new features, improve data pipeline reliability, and contribute to the shared libraries and infrastructure tooling that the whole engineering organisation depends on.

This is a hands‑on engineering role – we expect you to write production code, review others’ code, and take end‑to‑end ownership from design to deployment.

• Microservices – Kotlin & Spring Boot 3.x services
• Search & analytics – Open Search integration, Apache Parquet/Hadoop for data lake reads, Spring Batch jobs
• Data stores – PostgreSQL (RDS Aurora, Flyway migrations), Redis (Elasti Cache), DynamoDB, Amazon Redshift
• Identity & security – Keycloak (OAuth2 / OIDC), Spring Security resource servers, AWS KMS, Secrets Manager
• Infrastructure – Terraform‑managed AWS (ECS, ECR, Lambda, API Gateway, S3, SQS/SNS, SES, Glue, AWS Batch, Step Functions, Cloud Front, WAFv2), Git Lab CI/CD pipelines, Docker + Jib
• Observability – Prometheus, Grafana dashboards, AWS Cloud Watch alarms, structured logging

• 5+ years of backend engineering experience, with at least 3 years in the JVM ecosystem
• Strong Kotlin experience – coroutines, extension functions, sealed classes
• Production experience with Apache Kafka, ideally Kafka Streams, schema evolution, consumer group management
• Solid understanding of REST API design, event‑driven architecture, and distributed systems trade‑offs
• Confidence working with PostgreSQL – query optimisation, indexing, schema migrations (Flyway or similar)
• Experience deploying containerised services on AWS (ECS or EKS); familiarity with Terraform or another IaC tool
• Ability to own a feature end‑to‑end: RFC → implementation → testing → deployment → monitoring

• Operating systems: process/thread scheduling, memory management, file descriptors, signals
• Networking: TCP/IP, TLS handshake, HTTP/1.1 vs HTTP/2, DNS, load balancer behaviour, connection pooling

• SOLID, DRY, YAGNI – but more importantly, knowing when to break them
• Domain‑driven design: aggregates, bounded contexts, event sourcing concepts
• Testing strategy: knowing the difference between a unit, integration, and contract test, and when each pays off
• Evolutionary architecture: working safely in a codebase that must stay live 24/7 – feature flags, backwards‑compatible schema changes, strangler fig pattern
• Code review as a craft: giving feedback that improves the code without demoralising the author

• Advanced IDE usage (IntelliJ IDEA) – comfortable with refactoring tools, debugger, profiler, database console, and custom live templates; a keyboard‑first workflow
• Advanced AI‑assisted development – you actively use AI coding agents (Claude Code, Codex, Cursor) as a force multiplier: generating scaffolding, navigating unfamiliar codebases, writing test cases, and iterating on designs; you know when to trust the output and when to push back

• Exciting insights – work in an exciting and growing green start‑up and gain insights into the energy industry
• Realisation of ideas – an environment in which you can develop your skills and ideas and receive support
• Career opportunities – benefit from promising career opportunities and regular training programmes
• Fairness – an attractive salary package with options such as travel expenses, pension scheme, vouchers and more
• Flexibility – workations and flexible working models that adapt to your life
• Delicious snacks & drinks – cold drinks in the fridge and a wide range of tasty snacks
• Team activities – evening team drinks, table football, mindful and cooking sessions, boat party in summer
• Exclusive benefits – pool car, sharing marketplace or control of your heating and utility bills
• Language courses – improve your English or German skills with our language courses
• Unique office – industrial‑style office with a gym floor in Prenzlauer Berg, with very good transport links