Senior Java Software Engineer (Distributed systems)

Senior Java Software Engineer (Kafka, Security) – Messaging/Booking – Amsterdam Hourly rate: €50 - €100 Duration: 12 months Hybrid or Remote Start: ASAP My client is looking for 3 Senior Backend Engineers to join the team on a 12 month contract. As a Backend Software Engineer, you'll design, build, and operate Java-based backend services that power messaging security capabilities. You'll own solutions end-to-end from implementation and testing through deployment, monitoring, and production support. This role is ideal for a strong backend engineer who enjoys working with distributed systems, APIs, cloud-native technologies, and large-scale messaging infrastructure while solving complex security challenges. What You'll Do Design, develop, and maintain backend services using Java and modern engineering practices Build security capabilities that detect and prevent spam, phishing, malicious links, malicious attachments, and messaging abuse Work within a large existing Java codebase and contribute to long-term platform improvements Design and evolve APIs, ensuring strong developer experience and maintainable integration patterns Collaborate with messaging platform teams to integrate security controls into core messaging workflows Participate in system design discussions, evaluating solutions for scalability, reliability, and security Own services end-to-end, including deployment, monitoring, alerting, troubleshooting, and operational support Investigate production incidents, perform root cause analysis, and implement preventative solutions Improve service maturity through automated testing, observability, and continuous delivery practices Support the migration of legacy consumers from database-driven integrations to modern API-based solutions Required Strong experience building backend applications in Java (Java 17+ preferred) Experience developing and operating production services Ability to work effectively within large, established codebases Experience with microservices and distributed systems Familiarity with Kafka or similar messaging/streaming technologies Experience designing and consuming REST APIs Strong understanding of software engineering best practices, including testing, code reviews, and CI/CD Ability to work independently and take ownership of technical solutions Professional English communication skills Preferred Spring Boot or DropWizard AWS (EKS, S3, and related services) Kubernetes GitLab CI/CD and deployment orchestration tools OpenAPI specifications and API lifecycle management Grafana, Loki, OpenTelemetry, and distributed tracing Experience with high-throughput messaging systems GraphQL Security engineering, fraud prevention, abuse detection, or application security experience Understanding of spam detection, phishing protection, malicious file scanning, or link security Interest in AI/ML applications for security and threat detection