Serverless Offline

This Serverless plugin emulates AWS λ and API Gateway on your local machine to speed up your development cycles. To do so, it starts an HTTP server that handles the request's lifecycle like APIG does and invokes your handlers.

Features:

• Node.js, Python, Ruby λ runtimes.
• Velocity templates support.
• Lazy loading of your handler files.
• And more: integrations, authorizers, proxies, timeouts, responseParameters, HTTPS, CORS, etc...

This plugin is updated by its users, I just do maintenance and ensure that PRs are relevant to the community. In other words, if you find a bug or want a new feature, please help us by becoming one of the contributors ✌️ ! See the contributing section.

Documentation

• Installation
• Usage and command line options
• Usage with invoke
• Token authorizers
• Custom authorizers
• Remote authorizers
• Custom headers
• Environment variables
• AWS API Gateway features
• WebSocket
• Usage with Webpack
• Velocity nuances
• Debug process
• Scoped execution
• Simulation quality
• Credits and inspiration
• License
• Contributing

Installation

First, add Serverless Offline to your project:

npm install serverless-offline --save-dev

Then inside your project's serverless.yml file add following entry to the plugins section: serverless-offline. If there is no plugin section you will need to add it to the file.

It should look something like this:

plugins:
  - serverless-offline

You can check wether you have successfully installed the plugin by running the serverless command line:

serverless --verbose

the console should display Offline as one of the plugins now available in your Serverless project.

Usage and command line options

In your project root run:

serverless offline or sls offline.

to list all the options for the plugin run:

sls offline --help

All CLI options are optional:

--apiKey                    Defines the API key value to be used for endpoints marked as private Defaults to a random hash.
--corsAllowHeaders          Used as default Access-Control-Allow-Headers header value for responses. Delimit multiple values with commas. Default: 'accept,content-type,x-api-key'
--corsAllowOrigin           Used as default Access-Control-Allow-Origin header value for responses. Delimit multiple values with commas. Default: '*'
--corsDisallowCredentials   When provided, the default Access-Control-Allow-Credentials header value will be passed as 'false'. Default: true
--corsExposedHeaders        Used as additional Access-Control-Exposed-Headers header value for responses. Delimit multiple values with commas. Default: 'WWW-Authenticate,Server-Authorization'
--disableCookieValidation   Used to disable cookie-validation on hapi.js-server
--enforceSecureCookies      Enforce secure cookies
--hideStackTraces           Hide the stack trace on lambda failure. Default: false
--host                  -o  Host name to listen on. Default: localhost
--httpPort                  Http port to listen on. Default: 3000
--httpsProtocol         -H  To enable HTTPS, specify directory (relative to your cwd, typically your project dir) for both cert.pem and key.pem files
--lambdaPort                Lambda http port to listen on. Default: 3002
--noPrependStageInUrl       Don't prepend http routes with the stage.
--noAuth                    Turns off all authorizers
--noTimeout             -t  Disables the timeout feature.
--printOutput               Turns on logging of your lambda outputs in the terminal.
--resourceRoutes            Turns on loading of your HTTP proxy settings from serverless.yml
--useChildProcesses         Run handlers in a child process
--useWorkerThreads          Uses worker threads for handlers. Requires node.js v11.7.0 or higher
--websocketPort             WebSocket port to listen on. Default: 3001
--useDocker                 Run handlers in a docker container.

Any of the CLI options can be added to your serverless.yml. For example:

custom:
  serverless-offline:
    httpsProtocol: "dev-certs"
    httpPort: 4000

Options passed on the command line override YAML options.

By default you can send your requests to http://localhost:3000/. Please note that:

• You'll need to restart the plugin if you modify your serverless.yml or any of the default velocity template files.
• When no Content-Type header is set on a request, API Gateway defaults to application/json, and so does the plugin. But if you send an application/x-www-form-urlencoded or a multipart/form-data body with an application/json (or no) Content-Type, API Gateway won't parse your data (you'll get the ugly raw as input), whereas the plugin will answer 400 (malformed JSON). Please consider explicitly setting your requests' Content-Type and using separate templates.

Usage with invoke

To use Lambda.invoke you need to set the lambda endpoint to the serverless-offline endpoint:

const { Lambda } = require('aws-sdk')

const lambda = new Lambda({
  apiVersion: '2015-03-31',
  // endpoint needs to be set only if it deviates from the default, e.g. in a dev environment
  // process.env.SOME_VARIABLE could be set in e.g. serverless.yml for provider.environment or function.environment
  endpoint: process.env.SOME_VARIABLE
    ? 'http://localhost:3002'
    : 'https://lambda.us-east-1.amazonaws.com',
})

All your lambdas can then be invoked in a handler using

exports.handler = async function() {
  const params = {
    // FunctionName is composed of: service name - stage - function name, e.g.
    FunctionName: 'myServiceName-dev-invokedHandler',
    InvocationType: 'RequestResponse',
    Payload: JSON.stringify({ data: 'foo' }),
  }

  const response = await lambda.invoke(params).promise()
}

Token authorizers

As defined in the Serverless Documentation you can use API Keys as a simple authentication method.

Serverless-offline will emulate the behaviour of APIG and create a random token that's printed on the screen. With this token you can access your private methods adding x-api-key: generatedToken to your request header. All api keys will share the same token. To specify a custom token use the --apiKey cli option.

Custom authorizers

Only custom authorizers are supported. Custom authorizers are executed before a Lambda function is executed and return an Error or a Policy document.

The Custom authorizer is passed an event object as below:

{
  "type": "TOKEN",
  "authorizationToken": "<Incoming bearer token>",
  "methodArn": "arn:aws:execute-api:<Region id>:<Account id>:<API id>/<Stage>/<Method>/<Resource path>"
}

The methodArn does not include the Account id or API id.

The plugin only supports retrieving Tokens from headers. You can configure the header as below:

"authorizer": {
  "type": "TOKEN",
  "identitySource": "method.request.header.Authorization", // or method.request.header.SomeOtherHeader
  "authorizerResultTtlInSeconds": "0"
}

Remote authorizers

You are able to mock the response from remote authorizers by setting the environmental variable AUTHORIZER before running sls offline start

Example:

Unix: export AUTHORIZER='{"principalId": "123"}'

Windows: SET AUTHORIZER='{"principalId": "123"}'

Custom headers

You are able to use some custom headers in your request to gain more control over the requestContext object.

Header	Event key
cognito-identity-id	event.requestContext.identity.cognitoIdentityId
cognito-authentication-provider	event.requestContext.identity.cognitoAuthenticationProvider

By doing this you are now able to change those values using a custom header. This can help you with easier authentication or retrieving the userId from a cognitoAuthenticationProvider value.

Environment variables

You are able to use environment variables to customize identity params in event context.

Environment Variable	Event key
SLS_COGNITO_IDENTITY_POOL_ID	event.requestContext.identity.cognitoIdentityPoolId
SLS_ACCOUNT_ID	event.requestContext.identity.accountId
SLS_COGNITO_IDENTITY_ID	event.requestContext.identity.cognitoIdentityId
SLS_CALLER	event.requestContext.identity.caller
SLS_API_KEY	event.requestContext.identity.apiKey
SLS_COGNITO_AUTHENTICATION_TYPE	event.requestContext.identity.cognitoAuthenticationType
SLS_COGNITO_AUTHENTICATION_PROVIDER	event.requestContext.identity.cognitoAuthenticationProvider

You can use serverless-dotenv-plugin to load environment variables from your .env file.

AWS API Gateway Features

Velocity Templates

Serverless doc ~ AWS doc

You can supply response and request templates for each function. This is optional. To do so you will have to place function specific template files in the same directory as your function file and add the .req.vm extension to the template filename. For example, if your function is in code-file: helloworld.js, your response template should be in file: helloworld.res.vm and your request template in file helloworld.req.vm.

CORS

Serverless doc

If the endpoint config has CORS set to true, the plugin will use the CLI CORS options for the associated route. Otherwise, no CORS headers will be added.

Catch-all Path Variables

AWS doc

Set greedy paths like /store/{proxy+} that will intercept requests made to /store/list-products, /store/add-product, etc...

ANY method

AWS doc

Works out of the box.

Lambda and Lambda Proxy Integrations

Serverless doc ~ AWS doc

Works out of the box. See examples in the manual_test directory.

HTTP Proxy

Serverless doc ~ AWS doc - AWS::ApiGateway::Method ~ AWS doc - AWS::ApiGateway::Resource

Example of enabling proxy:

custom:
  serverless-offline:
    resourceRoutes: true

or

    YourCloudFormationMethodId:
      Type: AWS::ApiGateway::Method
      Properties:
        ......
        Integration:
          Type: HTTP_PROXY
          Uri: 'https://s3-${self:custom.region}.amazonaws.com/${self:custom.yourBucketName}/{proxy}'
          ......

custom:
  serverless-offline:
    resourceRoutes:
      YourCloudFormationMethodId:
        Uri: 'http://localhost:3001/assets/{proxy}'

Response parameters

AWS doc

You can set your response's headers using ResponseParameters.

May not work properly. Please PR. (Difficulty: hard?)

Example response velocity template:

"responseParameters": {
  "method.response.header.X-Powered-By": "Serverless", // a string
  "method.response.header.Warning": "integration.response.body", // the whole response
  "method.response.header.Location": "integration.response.body.some.key" // a pseudo JSON-path
},

WebSocket

Usage in order to send messages back to clients:

POST http://localhost:3001/@connections/{connectionId}

Or,

const apiGatewayManagementApi = new AWS.ApiGatewayManagementApi({
  apiVersion: '2018-11-29',
  endpoint: 'http://localhost:3001',
});

apiGatewayManagementApi.postToConnection({
  ConnectionId: ...,
  Data: ...,
});

Where the event is received in the lambda handler function.

There's support for websocketsApiRouteSelectionExpression in it's basic form: $request.body.x.y.z, where the default value is $request.body.action.

Authorizers and wss:// are currently not supported.

Usage with Webpack

Use serverless-webpack to compile and bundle your ES-next code

Velocity nuances

Consider this requestTemplate for a POST endpoint:

"application/json": {
  "payload": "$input.json('$')",
  "id_json": "$input.json('$.id')",
  "id_path": "$input.path('$').id"
}

Now let's make a request with this body: { "id": 1 }

AWS parses the event as such:

{
  "payload": {
    "id": 1
  },
  "id_json": 1,
  "id_path": "1" // Notice the string
}

Whereas Offline parses:

{
  "payload": {
    "id": 1
  },
  "id_json": 1,
  "id_path": 1 // Notice the number
}

Accessing an attribute after using $input.path will return a string on AWS (expect strings like "1" or "true") but not with Offline (1 or true). You may find other differences.

Debug process

Serverless offline plugin will respond to the overall framework settings and output additional information to the console in debug mode. In order to do this you will have to set the SLS_DEBUG environmental variable. You can run the following in the command line to switch to debug mode execution.

Unix: export SLS_DEBUG=*

Windows: SET SLS_DEBUG=*

Interactive debugging is also possible for your project if you have installed the node-inspector module and chrome browser. You can then run the following command line inside your project's root.

Initial installation: npm install -g node-inspector

For each debug run: node-debug sls offline

The system will start in wait status. This will also automatically start the chrome browser and wait for you to set breakpoints for inspection. Set the breakpoints as needed and, then, click the play button for the debugging to continue.

Depending on the breakpoint, you may need to call the URL path for your function in seperate browser window for your serverless function to be run and made available for debugging.

Resource permissions and AWS profile

Lambda functions assume an IAM role during execution: the framework creates this role and set all the permission provided in the iamRoleStatements section of serverless.yml.

However, serverless offline makes use of your local AWS profile credentials to run the lambda functions and that might result in a different set of permissions. By default, the aws-sdk would load credentials for you default AWS profile specified in your configuration file.

You can change this profile directly in the code or by setting proper environment variables. Setting the AWS_PROFILE environment variable before calling serverless offline to a different profile would effectively change the credentials, e.g.

AWS_PROFILE=<profile> serverless offline

Scoped execution

Downstream plugins may tie into the before:offline:start:end hook to release resources when the server is shutting down.

Simulation quality

This plugin simulates API Gateway for many practical purposes, good enough for development - but is not a perfect simulator. Specifically, Lambda currently runs on Node.js v10.x and v12.x (AWS Docs), whereas Offline runs on your own runtime where no memory limits are enforced.

Usage with serverless-dynamodb-local and serverless-webpack plugin

Run serverless offline start. In comparison with serverless offline, the start command will fire an init and a end lifecycle hook which is needed for serverless-offline and serverless-dynamodb-local to switch off resources.

Add plugins to your serverless.yml file:

plugins:
  - serverless-webpack
  - serverless-dynamodb-local
  - serverless-offline # serverless-offline needs to be last in the list

Credits and inspiration

This plugin was initially a fork of Nopik's Serverless-serve.

License

MIT

Contributing

Yes, thank you! This plugin is community-driven, most of its features are from different authors. Please update the docs and tests and add your name to the package.json file. We try to follow Airbnb's JavaScript Style Guide.

Contributors

dnalborczyk	dherault	computerpunc	leonardoalifraco	daniel-cottone

mikestaub	Bilal-S	dl748	frsechet	zoellner

johncmckim	ThisIsNoZaku	darthtrevino	miltador	gertjvr

juanjoDiaz	perkyguy	jack-seek	hueniverse	robbtraister

dortega3000	ansraliant	joubertredrat	andreipopovici	Andorbal

AyushG3112	franciscocpg	kajwiklund	ondrowan	sulaysumaria

jormaechea	awwong1	c24w	vmadman	encounter

Bob-Thomas	njriordan	bebbi	trevor-leach	emmoistner

OrKoN	adieuadieu	apalumbo	anishkny	cameroncooper

cmuto09	dschep	DimaDK24	dwbelliston	eabadjiev

Arkfille	garunski	james-relyea	joewestcott	LoganArnett

ablythe	marccampbell	purefan	mzmiric5	paulhbarker

pmuens	pierreis	ramonEmilio	rschick	selcukcihan

patrickheeney	rma4ok	clschnei	djcrabhat	adam-nielsen

adamelliottsweeting	againer	alebianco-doxee	koterpillar	triptec

constb	cspotcode	aliatsis	arnas	akaila

ac360	austin-payne	bencooling	BorjaMacedo	BrandonE

guerrerocarlos	chrismcleod	christophgysin	Clement134	rlgod

dbunker	dobrynin	domaslasauskas	enolan	minibikini

em0ney	erauer	gbroques	guillaume	balassy

idmontie	jacintoArias	jgrigg	jsnajdr	horyd

jaydp17	jeremygiberson	josephwarrick	jlsjonas	joostfarla

kenleytomlin	lalifraco-devspark	DynamicSTOP	medikoo	neverendingqs

msjonker	Takeno	mjmac	ojongerius	thepont

WooDzu	PsychicCat	Raph22	wwsno	gribnoysup

starsprung	shineli-not-used-anymore	stesie	stevemao	ittus

tiagogoncalves89	tuanmh	Gregoirevda	gcphost	YaroslavApatiev

zacacollier	allenhartwig	demetriusnunes	hsz	electrikdevelopment

jgilbert01	polaris340	kobanyan	leruitga-ss	livingmine

lteacher	martinmicunda	nori3tsu	ppasmanik	ryanzyy

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