REST API

REST API Overview

REST API is a building block you will reach for often in AWS Lambda. It keeps related logic together and makes your intent obvious to reviewers and future maintainers.

When you learn rest api properly, you avoid the guesswork that leads to bugs and rework. The example below shows the shape you will use in most real AWS Lambda projects.

export const handler = async (event) => {
  const { httpMethod, pathParameters, queryStringParameters } = event;
  const id = pathParameters?.id;

  if (httpMethod === 'GET') {
    return respond(200, { id, message: 'ok' });
  }

  return respond(405, { message: 'Method not allowed' });
};

function respond(statusCode, body) {
  return {
    statusCode,
    headers: { 'content-type': 'application/json' },
    body: JSON.stringify(body),
  };
}

This handler reads request details from the API Gateway event and returns a proxy-integration response.

REST API Example

// handler.mjs
export const handler = async (event, context) => {
  // 1. read input from the event
  // 2. do the work
  // 3. return a response (or throw on error)
};

• Start from a minimal REST API example and grow it only as needed.
• Keep configuration explicit so REST API behaves the same in every environment.
• Name things clearly so teammates understand your REST API at a glance.
• Add tests around REST API early to lock in expected behaviour.

AWS Lambda Cheatsheet

Handy reference for working with rest api in AWS Lambda and Node.js.

How REST API Works in AWS Lambda

REST API runs inside the managed Lambda execution environment. AWS provisions a micro-VM, loads your Node.js code, runs any module-scope initialisation once, and then invokes your handler for each event.

This handler reads request details from the API Gateway event and returns a proxy-integration response.

• Handlers should be small and do one job well.
• Initialise SDK clients and config outside the handler to reuse them on warm starts.
• Return quickly and let event sources handle retries where possible.
• Emit structured logs so CloudWatch and X-Ray can correlate activity.

Practical Guidance for REST API

On real projects, rest api works best when it is observable, secure, and cheap to run. Grant least-privilege IAM, validate every input, and keep the deployment package small.

Common Mistakes

• Copying rest api snippets without understanding what each line does.
• Skipping error handling and edge cases when wiring up rest api.
• Leaving rest api untested, so regressions slip into production.
• Over-engineering rest api before you actually need the extra flexibility.

Key Takeaways

• REST API is a core part of working effectively with AWS Lambda.
• Start small and keep rest api focused on a single responsibility.
• Apply consistent patterns so rest api scales across your project.
• Test and document rest api to keep it maintainable over time.