Senior Fullstack Engineer

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 take pride in our diverse and talented team and partners, spread across the UK, Cyprus, the Netherlands, and other regions worldwide.

We are currently looking for a Senior Fullstack Engineer for our flagship project, Happy Color.

Key Responsibilities:

• Design and develop microservices in Go/PHP (REST/gRPC), public and internal APIs.
• Develop frontend using TypeScript (React) with a focus on performance and Developer Experience (DX).
• Integrate with external services, develop contracts.
• Optimize performance, profiling, reduce latency, and scale systems.
• Design database schemas, perform migrations, indexing, and query optimization.
• 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/PHP and 3+ years with TypeScript.
• Strong frontend skills with TypeScript: React, state management (Redux Toolkit), routing, bundle formation, and optimization.
• Databases: PostgreSQL/MySQL, Redis; design, indexing, transactions.
• Queues/Buses: Kafka/NATS — experience in designing event-driven integrations.
• CI/CD: GitLab CI, feature flags, migrations, blue‑green/rolling deployments.
• Security: OAuth2, JWT.
• Understanding of DDD principles, SOLID, 12-factor methodology, observability (Prometheus/Grafana, OpenTelemetry).
• Russian - С1/higher, English - B1.

Nice to have:

• Testing: Jest, Playwright; for Go — testing/testify, integration/e2e.
• Data architecture: CQRS/Event Sourcing, idempotency, deduplication.
• Experience building BFFs, WebSockets.
• Feature flags, experiments/A-B testing, product metrics.

Technology Stack (Primary):

• Backend: Go, PHP, gRPC/REST, PostgreSQL, Redis, Kafka.
• Frontend: TypeScript, React, Redux Toolkit, Playwright.
• DevOps: GitLab CI, Docker, nice to have: Kubernetes, AWS, Helm.
• Observability: Prometheus, Grafana, Loki, OpenTelemetry, Sentry.

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 product together!

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