Kotlin Backend Engineer - (Freelance/Service Agreement)
Flix · Wrocław, Lower Silesian Voivodeship, Poland
Software Development · 1,001-5,000 employees
About the role
Design, develop, and maintain backend services using Kotlin and Spring Boot for a partner-facing ecosystem. Drive architectural modernization and improve system observability and reliability using DataDog and AWS.
What they look for
Requirements
Requires over 4 years of software engineering experience with JVM languages and commercial Kotlin expertise. Must be proficient in Spring Boot, REST APIs, and relational database design.
Full description
We are looking for a skilled Kotlin Backend Engineer for service agreement collaboration. B2B Sales & Distribution team builds and operates the backend platform powering Flix's 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
