Start with a clear request lifecycle
Keep routing, validation, business logic, persistence, and response formatting separate. This makes responsibilities easier to test and prevents controllers from becoming a second application hidden inside the HTTP layer.
Validate at the edge
Reject malformed input before it reaches domain logic. Use consistent schemas for body, query, and path parameters, and return errors that tell clients which field needs attention without exposing internal details.
Design for retries and duplicates
Networks fail and clients retry. For payments, orders, webhooks, and other state-changing operations, use idempotency keys or unique constraints so a repeated request cannot create repeated business effects.
Make dependency failures explicit
Databases, queues, and third-party services will occasionally be slow or unavailable. Add timeouts, bounded retries, circuit breakers where appropriate, and fallback behaviour that matches the business risk.
Build observability into the API
- Attach a request ID to logs and responses.
- Record latency by route and status code.
- Track dependency timing separately from total request time.
- Alert on error rates and saturation, not only server crashes.
Scale the simple things first
Before adding complex infrastructure, remove avoidable work from the request path, add database indexes, paginate large responses, cache stable reads, and move slow jobs to a queue. A measured bottleneck should drive the next architectural change.