Senior Backend Engineer (Go)

xflow; Warszawa; Hybrid; PLN 180,000 - 260,000; Full time

Benefits offered by this job

Flexible working hours

Remote/office options

Job summary

X-FLOW in Warsaw, Poland is seeking a Senior Backend Engineer (Go) to design and build scalable microservices for Happy Color. You will own API design, server-side logic, data modeling, and event-driven integrations with Kafka/NATS across PostgreSQL/MySQL and Redis, while shaping CI/CD pipelines and cloud infrastructure on AWS.

You will work with a modern tech stack, including OpenSearch and observability tooling, to ensure performance, reliability, and secure access with OAuth2/JWT.

Qualifications

• 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.

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.

Skills

Golang

Go concurrency

API design

Distributed systems

PostgreSQL/MySQL

Redis

Kafka/NATS

OpenSearch (plus)

CI/CD GitLab

Testing Go

OAuth2/JWT

DDD/SOLID/12-factor

Russian language

English language

Tools

GitLab CI

Docker

Kubernetes

AWS

Prometheus

Grafana

OpenTelemetry

Job description

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.