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🛠️ API Best Practices — Design, Security, Reliability & Operability


1. API Design & Modeling

  • Use nouns for resources: /products, /orders (not /getProducts).
  • Use plural resource names: /products instead of /product.
  • Keep endpoints RESTful: use HTTP verbs (GET/POST/PUT/PATCH/DELETE) to express actions.
  • Design predictable URIs: hierarchical and consistent (/stores/{storeId}/products/{productId}).
  • Support filtering, sorting, paging via query parameters (e.g. ?page=1&pageSize=20&sort=price_desc&filter=category:books).

2. Versioning & Compatibility

  • Version your API from day one. Common strategies:
    • URI versioning: /v1/products
    • Header versioning: Accept: application/vnd.myapi.v1+json
  • Backwards compatibility: never break existing contracts; deprecate gracefully with HTTP 301/410 or response headers.
  • Deprecation policy: announce, provide migration guide, and give a sunset period.

3. Contracts & Documentation

  • Use OpenAPI / Swagger to document endpoints, models, and examples.
  • Provide examples for requests and responses.
  • Auto-generate SDKs/clients if you support external consumers.
  • Document error formats, rate limits, pagination details, and auth flows.

4. Authentication & Authorization

  • Use HTTPS only — TLS everywhere.
  • Prefer token-based auth: OAuth2 / OpenID Connect for external APIs; JWTs for internal services with caution.
  • Use scopes/roles to limit access.
  • Handle token expiry & refresh securely (refresh token rotation for higher security).
  • Avoid sending sensitive data in URL (use headers/body).

5. Input Validation & Output Safety

  • Validate all inputs (size, types, ranges); fail early with clear error messages.
  • Whitelist validation (allow only expected fields) rather than blacklisting.
  • Sanitize inputs to avoid injections (SQL/NoSQL/command).
  • Use DTOs (request/response models) — don’t expose EF/DB entities directly.
  • Map entities to DTOs with tools like AutoMapper or manual mapping.

6. Error Handling & Status Codes

  • Use proper HTTP status codes:
    • 200 OK, 201 Created, 204 No Content (successes)
    • 400 Bad Request (validation), 401 Unauthorized, 403 Forbidden, 404 Not Found
    • 409 Conflict (unique constraint), 422 Unprocessable Entity (semantic errors)
    • 429 Too Many Requests, 500 Internal Server Error
  • Return structured error payloads (use RFC 7807 application/problem+json):
{
  "type": "https://example.com/probs/invalid-input",
  "title": "Invalid input",
  "status": 400,
  "detail": "Price must be > 0",
  "instance": "/products"
}
  • Don’t leak internal details (stack traces, DB errors) in responses.

7. Pagination, Filtering & Sorting

  • Always paginate large collections. Default page size + max limit (e.g., default=20, max=100).
  • Return paging metadata (total, page, pageSize), and consider Link headers for next/prev.
  • Allow flexible filtering but restrict expensive operations server-side.

8. Caching & Performance

  • Use HTTP caching: Cache-Control, ETag, and conditional GET (If-None-Match) for GET endpoints.
  • Cache frequently-read resources (CDN, reverse proxy, in-memory).
  • Compress responses (gzip/ Brotli).
  • Avoid N+1 queries — eager load or use optimized queries.
  • Add database indexes for frequent filters/sorts.

9. Transactions & Consistency

  • Keep endpoints idempotent where possible (PUT for full updates, idempotency keys for POST).
  • Use Unit of Work / transactions inside service layer for multi-step updates.
  • Prefer eventual consistency for distributed systems, and document it.

10. Rate Limiting & Throttling

  • Apply rate limits to protect services (global and per-user).
  • Expose limit headers so clients know remaining quota:
    • X-RateLimit-Limit, X-RateLimit-Remaining, X-RateLimit-Reset
  • Return 429 Too Many Requests for exceeded limits.

11. Logging, Monitoring & Observability

  • Log structured data (JSON logs) with correlation IDs.
  • Include request id / correlation id in logs and responses (X-Request-Id).
  • Expose metrics & health checks (/health, Prometheus metrics).
  • Use distributed tracing (OpenTelemetry) for cross-service traces.

12. Security Hardening

  • Enforce HTTPS & HSTS.
  • Validate and limit file uploads (size/type).
  • Use secure headers (CSP, X-Content-Type-Options, X-Frame-Options).
  • Mask sensitive data in logs (PII, passwords, tokens).
  • Rotate secrets and store them in secret managers (Azure Key Vault, AWS Secrets Manager).
  • Scan dependencies for vulnerabilities and patch regularly.

13. Testing

  • Unit tests for business logic and service layer.
  • Integration tests with an in-memory or test DB.
  • Contract tests for API consumers (Pact).
  • Load/performance tests to identify bottlenecks.

14. CI/CD & Releases

  • Automate builds, tests, and deployment.
  • Run static analysis & security scans in pipeline.
  • Deploy with blue/green or canary strategies for safer rollouts.
  • Automate DB migrations (careful with destructive changes).

15. Documentation & Developer Experience

  • Publish API docs (OpenAPI) and examples.
  • Provide SDKs or code samples for common languages.
  • Offer client-friendly error messages and examples.
  • Provide a sandbox environment for integration testing.

16. Data Privacy & Compliance

  • Comply with GDPR / local regulations: data minimization, consent, deletion endpoints.
  • Implement retention policies and secure backups.
  • Log access to sensitive data and audit when necessary.

17. Practical Tips & Patterns

  • Prefer POST for complex queries (when query string becomes huge), but document clearly.
  • Use PATCH for partial updates; prefer JSON Patch or a custom patch model.
  • Use ETags and optimistic concurrency for updates to prevent lost updates.
  • Support content negotiation if you plan multiple formats (JSON/MsgPack).
  • Offer health checks and readiness probes for orchestrators (Kubernetes).

Quick Checklist (copy to your README)

  • [ ] HTTPS enforced
  • [ ] OpenAPI spec published
  • [ ] Versioning implemented
  • [ ] Authentication & scopes in place
  • [ ] Input validation & DTOs used
  • [ ] Proper status codes + problem+json errors
  • [ ] Pagination, filtering, sorting supported
  • [ ] Rate limiting & caching applied
  • [ ] Structured logging + correlation id
  • [ ] Health checks & metrics exposed
  • [ ] Automated tests in CI pipeline
  • [ ] Secrets in secret manager

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