Building Serverless APIs: 10 Best Practices You Should Follow

Serverless doesn't mean no server — it means no server management. You still write code, design APIs, and handle errors. What changes is the operational overhead: scaling, patching, and capacity planning all become the platform's responsibility.

After helping hundreds of teams ship serverless APIs on moqapi.dev, here are the ten practices that separate weekend prototypes from production-grade systems.

1. Keep Functions Small and Focused

Each function should do one thing. A /users/:id GET handler reads a user; a /users POST handler creates one. Avoid mega-functions that branch on HTTP method — they're harder to test and impossible to fine-tune for memory or timeout.

2. Externalise Configuration

API keys, database URLs, feature flags — none of these belong in source code. Use environment variables and a secrets manager. moqapi.dev injects project-level env vars into every function at deploy time, keeping your source tree clean.

3. Minimise Cold Starts

Cold starts are the tax you pay for on-demand compute. Reduce them by:

• Keeping your deployment package small (tree-shake dependencies).
• Lazy-loading heavy modules (e.g., SDKs) only when needed.
• Using provisioned concurrency for latency-sensitive routes.

4. Design Idempotent Endpoints

Network retries happen. If a client sends the same POST twice, the API should return the same result — not create a duplicate resource. Use idempotency keys or upsert semantics.

5. Embrace Structured Logging

Plain-text console.log statements are useless at scale. Emit JSON logs with correlation IDs, timestamps, and request metadata so you can query them in any log aggregator.

6. Validate Inputs at the Edge

Never trust incoming data. Use schema validation (Zod, Joi, JSON Schema) before your function logic runs. Return 400 early — don't let bad data reach your database.

7. Use Layers for Shared Code

Utility functions, common middleware, and shared types should live in layers — not duplicated across every function. moqapi.dev's Layers feature lets you publish a shared package once and attach it to any function.

8. Set Reasonable Timeouts

A 30-second default timeout is generous. Most API calls should finish in under two seconds. Set tight timeouts and let the platform retry or queue longer work asynchronously.

9. Version Your APIs

Breaking changes are inevitable. Path-based versioning (/v1/users, /v2/users) is the simplest strategy and works well with serverless routing.

10. Monitor, Alert, Iterate

Deploy is not the finish line. Track p99 latency, error rates, and cold-start frequency. Set up alerts for regressions and review metrics weekly.

Wrapping Up

Serverless shortens the path from idea to production, but only if you follow disciplined engineering practices. Start with these ten, and you'll avoid the most common pitfalls that trip up growing teams.