Web Function sample applications

Every sample uses index.js as the entry file and listens on the host and port from AWS_LAMBDA_HTTP_ENDPOINT. Package the application with its production dependencies and deploy it from a versioned Amazon S3 object.

The following table lists each sample and what you can learn from it.

Sample	Use it to learn
Minimal Express application	Start an HTTP server with Express.
Hono API and static files	Serve API routes and static files with Hono.
Server-sent events	Stream server-sent events and stop work when the client disconnects.
Multi-Region verification route	Return the serving Region when validating multi-Region routing.

Minimal Express application

This framework-based sample is an alternative to the zero-dependency starter created by --hello-world. For the starter deployment, see Deploy and test your Web Function.

Install Express:

npm init -y
npm install express

Create index.js:

const express = require('express');
const app = express();
const [host, port] = (process.env.AWS_LAMBDA_HTTP_ENDPOINT || 'localhost:3000').split(':');

app.get('/', (request, response) => {
  response.send('Hello from Lambda Web Functions!');
});

app.listen(port, host);

For packaging guidance, see Package and deploy a sample.

Hono API and static files

Install the dependencies:

npm init -y
npm pkg set type=module
npm install hono @hono/node-server

Create index.js:

import { serve } from '@hono/node-server';
import { serveStatic } from '@hono/node-server/serve-static';
import { Hono } from 'hono';
import { secureHeaders } from 'hono/secure-headers';

const app = new Hono();
app.use(secureHeaders());
app.use('/static/*', serveStatic({ root: './' }));
app.get('/api/health', (context) => context.json({ status: 'ok' }));
app.notFound((context) => context.json({ error: 'not found' }, 404));

const [host, port] = (process.env.AWS_LAMBDA_HTTP_ENDPOINT || 'localhost:3000').split(':');

serve({ fetch: app.fetch, port: Number(port), hostname: host });

Put static files under a static directory and include the directory in the deployment package.

Server-sent events

Add the following route to an Express application:

app.get('/events', (request, response) => {
  response.setHeader('Content-Type', 'text/event-stream');
  response.setHeader('Cache-Control', 'no-cache');
  response.flushHeaders();

  const interval = setInterval(() => {
    response.write(`data: ${JSON.stringify({ time: Date.now() })}\n\n`);
  }, 1000);

  response.on('close', () => {
    clearInterval(interval);
  });
});

The request remains active until the application ends the response or the client disconnects. Set the revision timeout for the maximum stream duration. WebSocket upgrades are not supported.

Multi-Region verification route

Add a route that returns the Region in which the request executed:

app.get('/region', (request, response) => {
  response.json({
    region: process.env.AWS_REGION,
    requestId: request.get('lambda-web-request-id')
  });
});

Call the route from the client locations that matter to your application. For a MultiRegion endpoint, the selected Region comes from latency-based routing and can change. Do not use the execution environment as a session store.

Package and deploy a sample

npm ci --omit=dev
zip -r function.zip index.js package.json package-lock.json node_modules
aws s3 cp function.zip s3://amzn-s3-demo-bucket/samples/function.zip

Include other files that the selected sample uses, such as the static directory in the Hono sample. To create a revision that references the uploaded object, see Deploying Web Function code from Amazon S3 and Managing Web Function revisions. For the higher-level deploy workflow, see Creating a Web Function (AWS CLI). After the revision is Active and the endpoint serves it, send a request to the endpoint domain to confirm the sample responds. For test coverage beyond this smoke test, see Testing Lambda Web Functions.