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Inspired by the AWSLABS aws-serverless-express library tailor made for the Fastify web framework.

No use of internal sockets, makes use of Fastify's inject function.

Seems faster (as the name implies) than aws-serverless-express and aws-serverless-fastify 😉


$ npm i @fastify/aws-lambda


@fastify/aws-lambda can take options by passing them with : awsLambdaFastify(app, options)

property description default value
binaryMimeTypes Array of binary MimeTypes to handle []
enforceBase64 Function that receives the response and returns a boolean indicating if the response content is binary or not and should be base64-encoded undefined
serializeLambdaArguments Activate the serialization of lambda Event and Context in http header x-apigateway-event x-apigateway-context false (was true for <v2.0.0)
decorateRequest Decorates the fastify request with the lambda Event and Context request.awsLambda.event request.awsLambda.context true
decorationPropertyName The default property name for request decoration awsLambda
callbackWaitsForEmptyEventLoop See: Official Documentation undefined
retainStage Retain the stage part of the API Gateway URL false
pathParameterUsedAsPath Use a defined pathParameter as path (i.e. 'proxy') false
parseCommaSeparatedQueryParams Parse querystring with commas into an array of values. Affects the behavior of the querystring parser with commas while using Payload Format Version 2.0 true



const awsLambdaFastify = require('@fastify/aws-lambda')
const app = require('./app')

const proxy = awsLambdaFastify(app)
// or
// const proxy = awsLambdaFastify(app, { binaryMimeTypes: ['application/octet-stream'], serializeLambdaArguments: false /* default is true */ })

exports.handler = proxy
// or
// exports.handler = (event, context, callback) => proxy(event, context, callback)
// or
// exports.handler = (event, context) => proxy(event, context)
// or
// exports.handler = async (event, context) => proxy(event, context)


const fastify = require('fastify')

const app = fastify()
app.get('/', (request, reply) => reply.send({ hello: 'world' }))

if (require.main === module) {
  // called directly i.e. "node app"
  app.listen({ port: 3000 }, (err) => {
    if (err) console.error(err)
    console.log('server listening on 3000')
} else {
  // required as a module => executed on aws lambda
  module.exports = app

When executed in your lambda function we don't need to listen to a specific port, so we just export the app in this case. The lambda.js file will use this export.

When you execute your Fastify application like always, i.e. node app.js (the detection for this could be require.main === module), you can normally listen to your port, so you can still run your Fastify function locally.


Lambda arguments

The original lambda event and context are passed via Fastify request and can be used like this:

app.get('/', (request, reply) => {
  const event = request.awsLambda.event
  const context = request.awsLambda.context
  // ...

If you do not like it, you can disable this by setting the decorateRequest option to false.

Alternatively the original lambda event and context are passed via headers and can be used like this, if setting the serializeLambdaArguments option to true:

app.get('/', (request, reply) => {
  const event = JSON.parse(decodeURIComponent(request.headers['x-apigateway-event']))
  const context = JSON.parse(decodeURIComponent(request.headers['x-apigateway-context']))
  // ...

Lower cold start latency

Since AWS Lambda now enables the use of ECMAScript (ES) modules in Node.js 14 runtimes, you could lower the cold start latency when used with Provisioned Concurrency thanks to the top-level await functionality.

We can use this by calling the fastify.ready() function outside of the Lambda handler function, like this:

import awsLambdaFastify from '@fastify/aws-lambda'
import app from './app.js'
export const handler = awsLambdaFastify(app)
await app.ready() // needs to be placed after awsLambdaFastify call because of the decoration:

Here you can find the approriate issue discussing this feature.

⚡️Some basic performance metrics

@fastify/aws-lambda (decorateRequest : false) x 56,892 ops/sec ±3.73% (79 runs sampled)

@fastify/aws-lambda x 56,571 ops/sec ±3.52% (82 runs sampled)

@fastify/aws-lambda (serializeLambdaArguments : true) x 56,499 ops/sec ±3.56% (76 runs sampled)

serverless-http x 45,867 ops/sec ±4.42% (83 runs sampled)

aws-serverless-fastify x 17,937 ops/sec ±1.83% (86 runs sampled)

aws-serverless-express x 16,647 ops/sec ±2.88% (87 runs sampled)

Fastest is @fastify/aws-lambda (decorateRequest : false), @fastify/aws-lambda


  • For apps that may not see traffic for several minutes at a time, you could see cold starts
  • Stateless only
  • API Gateway has a timeout of 29 seconds, and Lambda has a maximum execution time of 15 minutes. (Using Application Load Balancer has no timeout limit, so the lambda maximum execution time is relevant)
  • If you are using another web framework beside Fastify (i.e. Connect, Express, Koa, Restana, Sails, Hapi, Restify) or want to use a more generic serverless proxy framework, have a look at: serverless-http or serverless-adapter

🎖Who is using it?

locize is using @fastify/aws-lambda

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