Written by Nelson Koning
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Serverless 101: The fastest path to your first AWS Lambda—using Function URLs

If you’re just getting into serverless, the most frictionless “hello world” you can ship today is an AWS Lambda exposed directly to the web with a Function URL. It’s a built‑in HTTPS endpoint—no API Gateway, no load balancer—so you can focus on code, not plumbing. As a bonus, Lambda now supports modern runtimes like Node.js 22 and Python 3.13, so you can start with up‑to‑date language features. (docs.aws.amazon.com)

What we’ll build:

Think of it like plugging a guitar straight into a small amp. You can jam immediately. If you later need a pedalboard (auth, routing, rate limiting), you can graduate to API Gateway. (docs.aws.amazon.com)

Why Function URLs for your first Lambda?

When should you use API Gateway instead? If you need custom domains, OAuth/Cognito, request/response transformations, throttling, or usage plans, API Gateway is the right tool. Treat Function URLs as the “quick start” and API Gateway as the “full stack.” (docs.aws.amazon.com)

Prerequisites

Step 1: Create a Lambda on Node.js 22

1) In the AWS Console, open Lambda and choose “Create function.” 2) Author from scratch:

Replace the default handler with this minimal HTTP handler:

// index.mjs or index.js
export const handler = async (event) => {
  const name = event.queryStringParameters?.name ?? "world";
  return {
    statusCode: 200,
    headers: { "content-type": "application/json" },
    body: JSON.stringify({
      message: `Hello, ${name}!`,
      method: event.requestContext?.http?.method,
      path: event.rawPath,
      query: event.queryStringParameters,
    }),
  };
};

Prefer Python? Lambda also supports Python 3.13, so you can do the same with a short Flask‑style handler. (aws.amazon.com)

Step 2: Add a Function URL (the magic switch)

1) In your function page, find “Function URL” and click “Create.” 2) Auth type: NONE (public) for the quickest test. You can switch to AWS_IAM when you’re ready. (docs.aws.amazon.com) 3) CORS: If you’ll call from a browser, configure it here (for example, AllowOrigins: *, AllowMethods: GET). Pro tip: let the URL manage CORS headers to avoid duplicate headers in responses. (docs.aws.amazon.com)

Save. You’ll get a URL that looks like: https://abc123.lambda-url.us-east-1.on.aws (docs.aws.amazon.com)

Step 3: Test it

From your terminal:

curl "https://<your-id>.lambda-url.<your-region>.on.aws/?name=Lambda"

You should see a JSON response with the greeting and details about your request.

Security note: Public URLs are great for demos and webhooks, but they are, well, public. For protected endpoints, set AuthType to AWS_IAM and sign requests with SigV4—or graduate to API Gateway for richer auth (Cognito, OAuth, custom authorizers) and traffic controls. (docs.aws.amazon.com)

Optional: Try response streaming (bigger, faster responses)

Traditional Lambda HTTP responses are buffered: you build the full payload (max 6 MB), then return it. Response streaming flips that around—you can start sending bytes immediately, and you can go up to 200 MB. It’s great for server‑rendered HTML, long‑running queries, or generating files on the fly. (docs.aws.amazon.com)

Two things to do:

// streaming.mjs
import { pipeline } from 'node:stream/promises';
import { Readable } from 'node:stream';

export const handler = awslambda.streamifyResponse(
  async (event, responseStream) => {
    // Stream a greeting in chunks (pretend this is a large dataset)
    const chunks = [
      "Hello ",
      (event.queryStringParameters?.name ?? "world"),
      "! Here comes some streamed data...\n",
      ...Array.from({ length: 5 }, (_, i) => `chunk ${i + 1}\n`)
    ];
    await pipeline(Readable.from(chunks), responseStream);
  }
);

Behind the scenes, response streaming works via the InvokeWithResponseStream API or a Function URL in ResponseStream mode; Lambda’s Node.js runtime provides the awslambda.streamifyResponse decorator. (docs.aws.amazon.com)

Pricing tip: the first 6 MB streamed per request is free; beyond that, you pay per GB streamed. The free tier also includes 100 GiB of HTTP response streaming per month. (aws.amazon.com)

Troubleshooting quick hits

Where to go next

The big picture

Function URLs remove nearly all ceremony from “hello serverless.” In a few clicks, you’ve got a live HTTPS endpoint backed by code that scales with demand and only bills while it runs. When you’re ready for the full stage rig—custom domains, auth flows, quotas, caching—API Gateway slots in neatly. Until then, enjoy the simplicity, turn up the volume slowly, and get your first tune out the door. (docs.aws.amazon.com)

Happy deploying!