Senior Backend Engineer (Java, Kafka Streams, AWS)

Senior / Staff Backend Engineer (Java, Kafka Streams, AWS)

Location: Kraków, hybrid
Contract: B2B or UoP
B2B budget: up to 210 PLN/h + VAT
Work model: around 3 days per week from the office

We are looking for a Senior or Staff Backend Engineer to join a small, high-impact engineering team building a large-scale, event-driven platform.

This is a hands-on role for someone who enjoys working close to real production systems: high-volume data flows, asynchronous processing, external integrations, reliability, observability and technical ownership.

You will join a team where the codebase and domain are evolving, so this is a good opportunity for an engineer who does not need every problem to be fully defined before getting started. You will be expected to investigate, create structure, improve standards and make pragmatic technical decisions.

What you will do

• Build and evolve backend services using Java and Spring Boot

• Design and maintain real-time event-processing flows using Kafka Streams

• Work with stream-processing concepts such as topologies, transformations, joins, aggregations, stateful processing and data routing

• Integrate external systems and infrastructure into a scalable internal platform

• Improve reliability, observability and production readiness of services handling high-volume data

• Investigate production issues, performance bottlenecks and data-flow problems

• Work with AWS, Kubernetes, PostgreSQL, MongoDB, Redis, Terraform and Helm

• Contribute to code reviews, architecture decisions, documentation and engineering standards

• Collaborate with product, platform and engineering stakeholders across an international environment

What we are looking for

• 7+ years of backend engineering experience

• Strong, current hands-on experience with Java and Spring Boot

• Deep practical experience with Kafka Streams in production
  This should go beyond Kafka producers/consumers and include work with stream-processing logic, joins, aggregations, windowing, state stores or topology design

• Background in event-driven, distributed or real-time systems

• Hands-on AWS experience, ideally with services such as EKS, S3, SQS, SNS, Kinesis or Lambda

• Experience with Kubernetes, containers and production deployment environments

• Good understanding of databases such as PostgreSQL, MongoDB and Redis

• Strong production mindset: monitoring, debugging, reliability, performance and incident investigation

• Ability to work independently in an evolving and not always fully documented technical environment

• Clear English communication skills and confidence explaining technical topics to both engineers and non-technical stakeholders

Nice to have

• Kotlin experience

• Experience with high-throughput data processing or streaming platforms

• Terraform, Helm, Prometheus, Grafana, Micrometer or similar observability tooling

• Experience in a small product team, scale-up or ownership-heavy engineering environment

• Familiarity with AI-assisted development tools

What you can expect

• A technically challenging role focused on real production systems rather than isolated feature delivery

• Strong ownership

• Small team setup with room to influence architecture, standards and ways of working

• International engineering environment

• Clear recruitment process focused on practical engineering discussions

Recruitment process

1. Introductory conversation with the Hiring Manager

2. Technical interview focused on Kafka/use cases and Java/code quality

3. Final discussion with senior technical leadership

The full company and product context will be shared during the first recruiter call.