Senior Java Backend Developer

SUMMARY 💰 130 - 150 PLN/h on B2B 💰 15 600 - 18 000 PLN gross on UoP 📍 Kraków (Hybrid - 3 days in the office / 2 days remote) 💼 Senior PROJECT Join an engineering team responsible for developing core backend services for a modern, cloud-native platform. As a Senior Java Backend Developer, you will build scalable and reliable services using Java, Spring Boot, and Apache Kafka, with a strong focus on event-driven architecture, asynchronous processing, APIs, and enterprise integrations. You will work on business-critical services and ensure they are maintainable, resilient, observable, and ready for production environments. YOU WILL Design and develop modular backend services using Java and Spring BootBuild event-driven and asynchronous solutions based on Apache KafkaImplement resilient messaging patterns such as outbox, idempotent consumers, retries, and dead-letter queuesDesign and develop REST APIs following agreed API standards and contract-first practicesImplement business logic, workflow automation, and rule-driven processingIntegrate services with internal and external systems using REST, messaging, Kafka Connect, CDC, and other integration patternsContribute to event and schema governance using Avro, JSON Schema, Schema Registry, or similar technologiesWork with relational databases using SQL, JPA/Hibernate, and transactional processingImprove performance, reliability, and scalability of backend services and event flowsSupport distributed tracing, monitoring, and troubleshooting across distributed systemsCollaborate with architects, QA, and platform teams to deliver production-ready solutions MUST HAVE Strong commercial experience with Java, preferably Java 17+Very good knowledge of Spring BootHands-on experience with Apache Kafka and event-driven systemsGood understanding of event-driven architecture and asynchronous processingKnowledge of messaging patterns such as retries, idempotency, dead-letter queues, and delivery guaranteesExperience designing and implementing REST APIs, ideally using OpenAPIGood understanding of distributed systems concepts, including ordering, eventual consistency, and failure handlingStrong experience with relational databases and SQLPractical knowledge of JPA/Hibernate, transactions, and database performance optimisationStrong understanding of OOP, clean architecture, and maintainable software designExperience troubleshooting performance and reliability issues in distributed or asynchronous systemsAbility to translate business requirements into reliable backend solutionsEnglish allowing effective communication in an international engineering environment NICE TO HAVE Experience with Kafka Connect, Debezium, and/or Change Data Capture (CDC)Experience with Avro, Schema Registry, or event schema governanceKnowledge of CQRS, Saga, and/or Event Sourcing patternsExperience with workflow or rules engines such as Camunda or DroolsFamiliarity with caching and enterprise integration patternsExperience with observability, distributed tracing, and monitoring of backend servicesExperience with cloud-native environments, particularly AWS or other public cloud platformsExperience integrating applications with AI models or AI platforms OUR OFFER The relocation package (4500 PLN total value) is paid in three installments (1500 PLN per month) if your permanent office presence is mandatory and you need to relocate from another city.Benefits: Extended medical care (over 2000 medical facilities in Poland, 80 in Kraków) for you and your family; Multisport card; Life insurance