Kotlin Backend Engineer - (Freelance/Service Agreement)

City: Warsaw
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 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
     

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Dear potential Flixie, 

At Flix, we are committed to fostering diversity and inclusion. To support this initiative, we invite all applicants to complete our demographic questions on voluntary basis. Your responses will be processed as anonymized data and not linked to your profile, and thus assessed for statistical purposes and internal research. 

If you prefer not to provide this information, simply click on "I do not wish to answer." Be assured that neither the decision not to participate nor your answers will have an impact on your application, and your answers will remain anonymous and unidentifiable to you individually. The decision on your application will be made independently from your participation and the information you provide. 

We appreciate your cooperation in advance! 

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