Senior Java Developer

Are you ready to take ownership of mission-critical backend systems in a high-load environment? We are looking for a Senior Java Developer to join our engineering team in Warsaw. This is a hybrid role with 3 days per week in the office, giving you the perfect balance between collaboration and flexibility. At Sigma Software, we value engineering excellence, multicultural teamwork, and delivering secure, high-performance solutions. Why join us? You’ll work on a large-scale platform serving millions of users, contribute to architectural decisions, and be part of a company where innovation and ownership are encouraged. CUSTOMER Our customer is a well-established international company in the iGaming industry, known for its engineering-driven culture and multicultural team distributed across multiple countries. Operating multiple brands across various markets, the company delivers secure, high-performance digital platforms recognized for reliability and scalability. PROJECT You will be part of an experienced engineering team responsible for developing and maintaining a large-scale platform built on a modern microservices architecture. The platform supports multiple brands and geographies and operates in a high-load environment with a strong focus on scalability, reliability, security, and performance. The work includes designing and developing backend services, improving system architecture, optimizing performance, and ensuring the stability and maintainability of distributed systems. Design, develop, and maintain backend services using Java and Spring Boot Ensure high availability, scalability, and performance of distributed systems Collaborate with cross-functional teams to define technical requirements and deliver solutions end-to-end Implement integrations with internal and external systems Participate in architectural discussions and contribute to system evolution in a microservices environment Monitor, troubleshoot, and optimize services in production Ensure compliance with security, operational, and engineering standards Drive continuous improvement in code quality, testing, and deployment practices 5+ years of commercial experience with Java and Spring Boot Strong experience with MySQL and Kafka Proven track record working with microservices architecture in high-traffic, high-load systems Experience developing high-performance backend solutions for transaction-heavy platforms Ownership mindset with ability to deliver services end-to-end Excellent communication skills in English (C1 level), both written and verbal Experience with Kotlin