Senior Backend Engineer (Go)

Location: Warsaw, Mazowieckie, Poland X-FLOW is a mobile game development company established in 2018. We gained recognition after the release of Happy Color , the most popular digital coloring book and one of the most successful ad-driven mobile apps in the world. We are currently looking for a Senior Backend Engineer (Go) for our flagship project, Happy Color. Key Responsibilities: • Design and develop microservices in Go (REST/gRPC), public and internal APIs. • Integrate with external services, develop contracts. • Optimize performance, profiling, reduce latency, and scale systems. • Design database schemas, perform migrations, indexing, and query optimization. • Work with PostgreSQL/MySQL, Redis, Kafka/NATS and event-driven integrations. • Implement and maintain CI/CD, cloud infrastructure (AWS) with Docker/Kubernetes. • Ensure quality: writing tests (unit/integration/e2e), code reviews, automation of checks. • Ensure observability and reliability: logging, metrics, alerting, tracing. • Participate in architectural design, RFCs/ADRs. Requirements: • 3+ years of commercial development experience, including 3+ years with Golang. • Proficient in Go: context handling, concurrency (goroutines/channels), profiling (pprof), gRPC/REST, generics, modularity. • Strong understanding of backend architecture, API design, microservices, and distributed systems. • Databases: PostgreSQL/MySQL, Redis; design, indexing, transactions. • Queues/Buses: Kafka/NATS — experience in designing event-driven integrations. • Experience with search technologies such as OpenSearch would be a plus. • CI/CD: GitLab CI, feature flags, migrations, blue-green/rolling deployments. • Testing: Go testing/testify, integration/e2e. • Security: OAuth2, JWT. • Understanding of DDD principles, SOLID, 12-factor methodology, observability (Prometheus/Grafana, OpenTelemetry). • Russian - C1/higher, English - B1. Nice to have: • Experience with Python and/or PHP. • Experience with TypeScript, JavaScript and React. • Experience with OpenSearch. • Data architecture: CQRS/Event Sourcing, idempotency, deduplication. • Experience building BFFs, WebSockets. • Feature flags, experiments/A-B testing, product metrics. Technology Stack (Primary): • Backend: Go, gRPC/REST, PostgreSQL, Redis, Kafka. • DevOps: GitLab CI, Docker, nice to have: Kubernetes, AWS, Helm. • Observability: Prometheus, Grafana, Loki, OpenTelemetry, Sentry. • Search: OpenSearch. What We Offer: • Competitive salary and benefits package. • Opportunity to work with a talented and passionate team in a creative and dynamic environment. • Flexible working hours and remote/office work options. • Career growth and professional development opportunities. • A fun and inclusive company culture that celebrates diversity and creativity. Join us and let’s create great content together! When you apply for this role, we process your personal data in accordance with our Candidate Privacy Notice ( https://xflowgames.com/candidate-privacy-notice) .