Senior Java Backend Engineer at LoopMe Ltd · Krakow

Are you eager to work with advanced technologies and build high-performance applications capable of processing over 5 million requests per second? If yes, we have an ideal opportunity for you at LoopMe.

We are a team of experienced engineers developing and supporting real-time bidding platforms for global advertisers. You will work daily with talented engineers, using technologies such as Java, Spring Boot, gRPC, Project Reactor, Kafka, ClickHouse, PostgreSQL, Aerospike, and Redis. Your main focus will be on enhancing performance, optimizing cloud infrastructure, and developing innovative features across our product range.

Join us in our mission to expand the limits of possibilities in the advertising industry!

We are seeking a Senior Java Backend Engineer to join our Marketplace team and help develop our high-load ad-serving system, which can process more than 5 million requests per second with a 200ms response time.

What you’ll be doing

• Designing and tuning hot-path components for the ad-serving critical path—such as throttling, rate limiting, targeting indexes, and DSP adapters.
• Implementing architectural changes across services — including RTB request lifecycle, deals targeting, and multi-impression-key processing.
• Creating gRPC APIs and Protocol Buffers schemas to facilitate cross-team integrations.
• Profiling and minimizing CPU usage and allocations to achieve strict p99 latency goals.
• Strengthening the system architecture to guarantee smooth operation during peak load times.
• Integrating advanced targeting algorithms into the main ad delivery process.
• Collaborating closely with multiple teams to provide services and data for our solutions.

Core qualifications

• Over five years of experience in backend engineering.
• Solid understanding of Java and Spring / Spring Boot.
• Hands-on experience with SQL and familiarity with PostgreSQL or other relational databases.
• Strong knowledge of microservices architecture and its best practices.
• Proficient in Linux shell and Docker.

Additional experience we’d value

• Concurrency in Java includes java.util.concurrent, CompletableFuture, lock-free data structures, virtual threads / Project Loom, and Reactor schedulers.
• gRPC and Protocol Buffers
• Project Reactor / Spring WebFlux
• Kafka
• Kubernetes
• Experience in managing high-QPS services, including profiling with JFR and async-profiler, GC tuning, and JVM internals understanding.
• Robust testing culture with unit tests, functional tests, and Testcontainers.

Extra pluses

• AdTech / RTB domain expertise — OpenRTB, DSP/SSP, IVT, deals, cookie-sync, ads.txt, schain
• Performance engineering on critical paths — utilizing fastutil / Eclipse Collections, creating allocation-aware code, and optimizing for JIT awareness.
• Distributed systems experience includes rate-limiting algorithms such as token bucket, fixed and slidingwindow, as well as back-pressure, circuit breakers, sharding, and consistent hashing.
• Observability tools include Micrometer, Prometheus, Grafana, and structured logging.
• Full responsibility for managing multi-week epics across multiple teams.
• Experience with analytical or in-memory databases such as ClickHouse, Aerospike, Redis.

Benefits

• Flexible working schedule with a hybrid type of work
• Annual performance bonus
• One month of workation (you can work from any part of the world for one month)
• Multikafeteria