Kotlin Backend Engineer - (Freelance/Service Agreement)

Kotlin Backend Engineer - (Freelance/Service Agreement)

City: Kraków

Department: IT & Engineering

Recruiter: Anna Symonenko

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We are looking for a skilled Kotlin Backend Engineer for service agreement collaboration. B2B Sales & Distribution team builds and operates the backend platform powering Flixs partner-facing ecosystem — including a self-management platform for partners, a back office portal for internal users, and an AI agentic bot supporting partner operations. The team is driving a significant modernization of its backend architecture and is working in an AI-native development environment.

Scope of services

Independent delivery of backend services in Kotlin and Spring Boot, including design, development, and maintenance

Building and maintaining REST APIs used by internal and external partners

Contributing to architectural decisions and technical modernization initiatives as a senior topic driver

Improving observability, performance, and reliability of backend systems using DataDog

Supporting CI/CD pipelines and cloud infrastructure on AWS and Kubernetes

Working within an AI-native development environment, including CI-integrated code review automation and an internal Claude Code plugin marketplace covering Kotlin/Spring Boot conventions, architectural patterns, testing practices, and database guidelines

Sharing Kotlin expertise and best practices with existing engineers on the Flix team who are transitioning from other languages, through code review, pairing, and technical guidance

Relevant expertise

4+ years of software engineering experience, primarily backend development with a JVM language, including some commercial experience with Kotlin

Hands-on Spring Boot experience

Experience building and maintaining REST APIs and distributed systems

Solid SQL knowledge and relational database design, including MySQL and PostgreSQL

Sound software engineering fundamentals and clean code practices

Clear written and spoken English communication skills

Preferred experience with: AWS, Kubernetes, GitLab CI/CD, Kafka, Terraform, LLM integrations, RAG systems, AI product development, or legacy system migration experience

Collaboration model

Cooperation based on a service agreement with independent delivery of agreed services and invoicing

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