B2B | Hybrid | Location: Gdańsk or Warsaw (1–2 times every two months in the office )Project: Modernization of a banking systemRate: 30-50€/hWe’re looking for a Java Engineer/Data Engineer to join a project focused on modernizing and optimizing a long-standing legacy system. The current architecture cannot keep up with growing business demands, and the goal is to reach ~2,500 requests per second through deep analysis, refactoring, and architectural improvements.You will work in a team of 6 experienced engineers on 4 microservices, playing a key role in performance engineering. data integration, and modernization of Kafka-based components.Responsibilities: Analyze current performance and implement improvements to achieve target throughput (~2,500 req/s). Optimize communication between microservices and work with distributed systems. Improve data flows (Kafka) and refactor legacy components. Develop APIs and service components. Collaborate closely with the team in a client-facing environment. Address data quality and consistency issues.

Prepare the system for increased load with a deadline in April 2026.

Requirements: Minimum 5 years of experience as a Java Engineer / Data Engineer. Strong experience with Java 21 and the Spring Framework (ideally v3). Solid, hands-on experience with Apache Kafka, especially in distributed systems. Must understand internal Kafka mechanisms and know how to diagnose and resolve performance issues. Experience with databases, optimization, and potentially sharding. Experience in API development and data engineering (data transmission and processing). Strong knowledge of architectural patterns (DDD, event-driven, CQRS, etc.). Experience creating load tests with Kafka is a strong plus. About Scalac: For over 10 years, Scalac has been delivering high-quality software, successfully aiding FinTechs, HealthTechs, EdTechs, AdTechs, and startups in their efforts to scale. What’s our secret? There is none - just choosing the best technologies and connecting you with the top specialists to implement them. All done by working remotely! With over 50 experts on board, from 13 different countries - in Scala, Java, Spark, Rust, Akka, React, Angular, Kafka, blockchain, and more - there is no project we couldn’t enhance, no process we’re not able to support, and no software we couldn’t deliver from start to finish.Sounds like a fit?Apply now and join our team!