Introduction

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 😉

👨🏻‍💻Installation

$ npm i @fastify/aws-lambda

Options

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

property	description	default value
binaryMimeTypes	Array of Content-Type values to treat as binary (base64-encoded for API Gateway). See Binary responses.	[]
enforceBase64	Function (res) => boolean that decides whether the response body should be base64-encoded. When omitted, a built-in default base64-encodes any response with a non-identity Content-Encoding (i.e. gzip, br, deflate, zstd, …). See Binary responses.	undefined (falls back to a Content-Encoding-aware default)
disableBase64Encoding	Disable base64 encoding of responses and omit the isBase64Encoded property. When undefined, it is automatically enabled when payloadAsStream is true and the request does not come from an ALB.	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
payloadAsStream	If set to true the response is a stream and can be used with awslambda.streamifyResponse	false
albMultiValueHeaders	Set to true if using ALB with multi value headers attribute	false

Binary responses

API Gateway needs to know when a response body is binary so it can be base64-encoded over the wire (isBase64Encoded: true in the Lambda return payload). @fastify/aws-lambda decides this via two complementary paths — at least one match triggers base64 encoding:

• binaryMimeTypes — matches the response Content-Type against an allowlist. Use this when binary-ness is a property of the content type itself (e.g. application/octet-stream, image/png, application/zip).
• enforceBase64 — a function called with the response. Use this when binary-ness depends on something other than Content-Type — most commonly when the body is compressed (binary bytes) but the content type itself is text-like (e.g. application/json with Content-Encoding: br).

When enforceBase64 is omitted, a built-in default kicks in that base64-encodes any response with a non-identity Content-Encoding. So compressed responses (gzip, br, deflate, zstd, …) work out of the box — you don't need to write your own callback for the common case.

Example — let compressed responses pass through automatically

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

const app = fastify()
app.register(compress, { global: true, encodings: ['br', 'gzip'] })
app.get('/', (req, reply) => reply.send({ hello: 'world' }))

// Responses gain Content-Encoding: br|gzip, and the default behaviour
// auto-base64-encodes them for API Gateway. No extra option needed.
exports.handler = awsLambdaFastify(app)

Example — add a custom rule on top of the default

exports.handler = awsLambdaFastify(app, {
  binaryMimeTypes: ['application/octet-stream', 'image/png'],
  // Custom rule for binary detection. Note: when you pass enforceBase64,
  // it REPLACES the built-in Content-Encoding default — it doesn't compose.
  // Re-implement the compression check yourself if you still want it.
  enforceBase64: (res) => {
    if (res.headers['content-type'] === 'application/x-protobuf') return true
    const enc = res.headers['content-encoding']
    return !!enc && enc !== 'identity'
  }
})

📖Example

lambda.js

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)

app.js

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.

📣Hint

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: https://github.com/fastify/aws-lambda-fastify/blob/main/index.js#L9

Here you can find the approriate issue discussing this feature.

Support for response streaming (payloadAsStream)

import awsLambdaFastify from '@fastify/aws-lambda'
import { promisify } from 'node:util'
import stream from 'node:stream'
import app from './app.js'

const pipeline = promisify(stream.pipeline)
const proxy = awsLambdaFastify(app, { payloadAsStream: true })
export const handler = awslambda.streamifyResponse(async (event, responseStream, context) => {
  const { meta, stream } = await proxy(event, context)
  responseStream = awslambda.HttpResponseStream.from(responseStream, meta)
  await pipeline(stream, responseStream)
})
await app.ready() // https://github.com/fastify/aws-lambda-fastify/issues/89

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

⚠️Considerations

• 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?

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