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 teambuilds 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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