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Flix

Kotlin Backend Engineer - (Freelance/Service Agreement)

Flix · Krakow, Lesser Poland Voivodeship, Poland

Software Development · 1,001-5,000 employees

6 h ago
Mid (2-5 yrs) Contractor Poland
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About the role

You will independently design, develop, and maintain backend services using Kotlin and Spring Boot while contributing to architectural modernization. Additionally, you will support CI/CD pipelines, cloud infrastructure on AWS, and share technical expertise with the team.

What they look for

Kotlin Spring Boot Backend Development REST APIs AWS Kubernetes SQL MySQL PostgreSQL DataDog CI/CD GitLab Kafka Terraform Distributed Systems Clean Code

Requirements

Candidates must have 4+ years of backend development experience with a JVM language, specifically Kotlin and Spring Boot. Strong knowledge of SQL, REST APIs, and distributed systems is required, along with clear English communication skills.

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