What are microservice API best practices?

Here's a solid rundown of microservice API best practices:

Design & contracts

Design APIs contract-first (OpenAPI/Swagger, or protobuf for gRPC) so contracts are reviewable and code-generatable before implementation starts.

Version your APIs explicitly (URI versioning like /v1/, or header-based) and never break existing consumers without a deprecation window.

• Keep each service's API scoped to a single bounded context — don't let one service's endpoint become a dumping ground for unrelated functionality. Use consistent, predictable naming and resource structures across all services so consumers aren't relearning conventions service to service.

Gateway & routing

Put an API gateway in front of your services to centralize auth, rate limiting, routing, and request/response transformation instead of duplicating that logic in every service.

• Keep the gateway thin — routing, auth, and rate limiting belong there; business logic and data aggregation belong in the services (or a dedicated BFF layer) instead. Use service discovery (Consul, Eureka, Kubernetes DNS) rather than hardcoding service locations.

Resilience

Implement circuit breakers (e.g., via Istio, Envoy, or libraries like resilience4j) so one failing service doesn't cascade and take down callers.

• Set sensible timeouts and retries with backoff — infinite retries or no timeouts are a common cause of outages.
• Design for graceful degradation: return partial or cached data rather than failing entirely when a downstream dependency is unavailable. Use bulkheads/isolation so a spike in one service's traffic can't exhaust shared resources needed by others.

Security

Authenticate and authorize at the gateway (OAuth 2.0/OIDC, JWT validation) so individual services don't each reimplement auth.

Use mutual TLS (mTLS) for service-to-service communication inside the mesh, not just at the edge.

• Apply the principle of least privilege — services should only be able to call the specific downstream services/endpoints they actually need.

Observability

• Instrument distributed tracing (OpenTelemetry, Jaeger, Zipkin) so you can follow a single request across service boundaries — this is non-negotiable once you have more than a handful of services. Standardize structured logging with correlation/request IDs across all services.

Expose health checks (/healthz, /readyz) and metrics endpoints for orchestration and alerting.

Data & communication patterns

• Avoid shared databases between services — each service should own its data, and other services should only get it via the API. Use asynchronous messaging (Kafka, RabbitMQ, SQS) for cross-service workflows that don't need an immediate synchronous response, to reduce tight coupling.

Prefer eventual consistency and event-driven patterns (like the Saga pattern) over distributed transactions for cross-service data changes.

Implement idempotency keys on write operations, since retries and network failures are inevitable in distributed systems.

Documentation & developer experience

• Auto-generate docs from your API spec and keep them in sync with actual behavior — stale docs are worse than none. Provide a sandbox/staging environment so consuming teams can test against realistic behavior without hitting production.

Communicate breaking changes and deprecations well in advance, with a clear migration path.

Want me to tailor this list toward a specific client's stack or angle (e.g., if the query set is aimed at a particular gateway/API-management vendor)?