Senior Node.js Software Engineer

This position is ideal for a Senior Backend Engineer with 5+ years of experience in Node.js, TypeScript, and frameworks like Express.js or Fastify. Candidates should be proficient in SQL, API design (REST/GraphQL), Kafka, and have experience with monolith and microservice architectures. Familiarity with Go or frontend frameworks like Angular/React is a plus, as well as strong testing and architectural design skills.

1. Express vs Fastify—when would you choose one over the other?
   Fastify provides better throughput and a schema-driven approach (JSON Schema) with built-in validation and serialization; Express has a larger ecosystem and is simpler for quick setups. For high-performance APIs, prefer Fastify; for legacy/middleware-heavy apps, Express can be more convenient.

2. How do you design a TypeScript-safe HTTP handler?
   Define request/response types (e.g., with @fastify/type-provider-typebox or Zod) and use generics to bind route schemas to handler types. This ensures compile-time safety for params, query, body, and response.

3. REST vs GraphQL vs gRPC—trade-offs?
   REST is simple and cache-friendly but can over/under-fetch; GraphQL gives clients precise data at the cost of server complexity and caching challenges. gRPC is ideal for internal service-to-service low-latency calls with strong contracts via Protobuf.

4. What SQL techniques improve performance and correctness?
   Create composite indexes aligned with query filters/sort order, use proper normalization with selective denormalization, and keep transactions short. Tune connection pooling and understand isolation levels (e.g., READ COMMITTED vs REPEATABLE READ) to avoid deadlocks and anomalies.

5. How would you consume Kafka safely at scale?
   Partition topics for parallelism, use consumer groups for horizontal scaling, and commit offsets after processing to achieve at-least-once semantics. For exactly-once workflows, use idempotent producers and Kafka transactions with idempotent handlers.

6. Monolith vs microservices—when and how to split?
   Start with a well-modularized monolith; split when independent scaling, deployment cadence, or ownership demands it. Use the Strangler pattern, define clear domain boundaries, and formalize contracts (OpenAPI/Protobuf).

7. How do you structure tests with Jest/Supertest (or Mocha/Chai)?
   Unit-test pure logic with mocks; integration-test routes against a real or Testcontainers-backed DB plus Supertest for HTTP. Aim for deterministic tests and use fixtures/factories to keep suites fast and reproducible.

8. What patterns ensure API robustness under load?
   Apply caching (Redis, HTTP ETag/Cache-Control), rate limiting/sliding window, circuit breakers, retries with backoff, and idempotency keys for unsafe methods. Use pagination (cursor-based for large datasets) with matching DB indexes.

9. How do you implement observability for Node.js services?
   Emit structured logs (correlation IDs), metrics (RED: rate, errors, duration), and distributed traces via OpenTelemetry. Add health/readiness probes and alert on SLOs with error-budget burn rates.

10. How do Node.js and Go services interoperate effectively?
    Use gRPC/Protobuf or well-versioned REST with consistent auth (mTLS/JWT) and shared schemas. Keep contracts backward compatible and validate at CI with contract tests.

SoftServe is hiring a Senior Node.js Software Engineer to join a remote team supporting greenfield mobile app projects. You'll design scalable backend services using Node.js, TypeScript, Kafka, and SQL, while integrating APIs via REST, GraphQL, or gRPC. The role spans Bulgaria, Poland, or Romania, offering cross-functional collaboration, modern tech, and impactful global projects. Join a 2,000+ project leader transforming customer feedback into product innovation.