Serverless Step Functions

This is the Serverless Framework plugin for AWS Step Functions.

Install

Run npm install in your Serverless project.

$ npm install --save-dev serverless-step-functions

Add the plugin to your serverless.yml file

plugins:
  - serverless-step-functions

Setup

Specifies your statemachine definition using Amazon States Language in a definition statement in serverless.yml. We recommend to use serverless-pseudo-parameters plugin together so that it makes it easy to set up Resource section under definition.

functions:
  hellofunc:
    handler: handler.hello

stepFunctions:
  stateMachines:
    hellostepfunc1:
      events:
        - http:
            path: gofunction
            method: GET
        - schedule:
            rate: rate(10 minutes)
            enabled: true
            input:
              key1: value1
              key2: value2
              stageParams:
                stage: dev
      name: myStateMachine
      definition:
        Comment: "A Hello World example of the Amazon States Language using an AWS Lambda Function"
        StartAt: HelloWorld1
        States:
          HelloWorld1:
            Type: Task
            Resource: arn:aws:lambda:#{AWS::Region}:#{AWS::AccountId}:function:${self:service}-${opt:stage}-hello
            End: true
    hellostepfunc2:
      definition:
        StartAt: HelloWorld2
        States:
          HelloWorld2:
            Type: Task
            Resource: arn:aws:states:#{AWS::Region}:#{AWS::AccountId}:activity:myTask
            End: true
  activities:
    - myTask
    - yourTask

plugins:
  - serverless-step-functions
  - serverless-pseudo-parameters

Adding a custom name for a stateMachine

In case you need to interpolate a specific stage or service layer variable as the stateMachines name you can add a name property to your yaml.

service: messager

functions:
  sendMessage:
    handler: handler.sendMessage

stepFunctions:
  stateMachines:
    sendMessageFunc:
      name: sendMessageFunc-${self:custom.service}-${opt:stage}
      definition:
        <your definition>

plugins:
  - serverless-step-functions

Current Gotcha

Please keep this gotcha in mind if you want to reference the name from the resources section. To generate Logical ID for CloudFormation, the plugin transforms the specified name in serverless.yml based on the following scheme.

Transform a leading character into uppercase
Transform - into Dash
Transform _ into Underscore

If you want to use variables system in name statement, you can't put the variables as a prefix like this:${self:service}-${opt:stage}-myStateMachine since the variables are transformed within Output section, as a result, the reference will be broken.

The correct sample is here.

stepFunctions:
  stateMachines:
    myStateMachine:
      name: myStateMachine-${self:service}-${opt:stage}
...

resources:
  Outputs:
    myStateMachine:
      Value:
        Ref: MyStateMachineDash${self:service}Dash${opt:stage}

Events

API Gateway

To create HTTP endpoints as Event sources for your StepFunctions statemachine

Simple HTTP Endpoint

This setup specifies that the hello statemachine should be run when someone accesses the API gateway at hello via a GET request.

Here's an example:

stepFunctions:
  stateMachines:
    hello:
      events:
        - http:
            path: hello
            method: GET
      definition:

HTTP Endpoint with Extended Options

Here You can define an POST endpoint for the path posts/create.

stepFunctions:
  stateMachines:
    hello:
      events:
        - http:
            path: posts/create
            method: POST
      definition:

Enabling CORS

To set CORS configurations for your HTTP endpoints, simply modify your event configurations as follows:

stepFunctions:
  stateMachines:
    hello:
      events:
        - http:
            path: posts/create
            method: POST
            cors: true
      definition:

Setting cors to true assumes a default configuration which is equivalent to:

stepFunctions:
  stateMachines:
    hello:
      events:
        - http:
            path: posts/create
            method: POST
            cors:
              origin: '*'
              headers:
                - Content-Type
                - X-Amz-Date
                - Authorization
                - X-Api-Key
                - X-Amz-Security-Token
                - X-Amz-User-Agent
              allowCredentials: false
      definition:

Configuring the cors property sets Access-Control-Allow-Origin, Access-Control-Allow-Headers, Access-Control-Allow-Methods,Access-Control-Allow-Credentials headers in the CORS preflight response.

Send request to an API

You can input an value as json in request body, the value is passed as the input value of your statemachine

$ curl -XPOST https://xxxxxxxxx.execute-api.us-east-1.amazonaws.com/dev/posts/create -d '{"foo":"bar"}'

Setting API keys for your Rest API

You can specify a list of API keys to be used by your service Rest API by adding an apiKeys array property to the provider object in serverless.yml. You'll also need to explicitly specify which endpoints are private and require one of the api keys to be included in the request by adding a private boolean property to the http event object you want to set as private. API Keys are created globally, so if you want to deploy your service to different stages make sure your API key contains a stage variable as defined below. When using API keys, you can optionally define usage plan quota and throttle, using usagePlan object.

Here's an example configuration for setting API keys for your service Rest API:

service: my-service
provider:
  name: aws
  apiKeys:
    - myFirstKey
    - ${opt:stage}-myFirstKey
    - ${env:MY_API_KEY} # you can hide it in a serverless variable
  usagePlan:
    quota:
      limit: 5000
      offset: 2
      period: MONTH
    throttle:
      burstLimit: 200
      rateLimit: 100
functions:
  hello:
    handler: handler.hello

    stepFunctions:
      stateMachines:
        statemachine1:
          name: ${self:service}-${opt:stage}-statemachine1
          events:
            - http:
                path: /hello
                method: post
                private: true
          definition:
            Comment: "A Hello World example of the Amazon States Language using an AWS Lambda Function"
            StartAt: HelloWorld1
            States:
              HelloWorld1:
                Type: Task
                Resource: arn:aws:lambda:#{AWS::Region}:#{AWS::AccountId}:function:${self:service}-${opt:stage}-hello
                End: true


    plugins:
      - serverless-step-functions
      - serverless-pseudo-parameters

Please note that those are the API keys names, not the actual values. Once you deploy your service, the value of those API keys will be auto generated by AWS and printed on the screen for you to use. The values can be concealed from the output with the --conceal deploy option.

Clients connecting to this Rest API will then need to set any of these API keys values in the x-api-key header of their request. This is only necessary for functions where the private property is set to true.

Schedule

The following config will attach a schedule event and causes the stateMachine crawl to be called every 2 hours. The configuration allows you to attach multiple schedules to the same stateMachine. You can either use the rate or cron syntax. Take a look at the AWS schedule syntax documentation for more details.

stepFunctions:
  stateMachines:
    crawl:
      events:
        - schedule: rate(2 hours)
        - schedule: cron(0 12 * * ? *)
      definition:

Enabling / Disabling

Note: schedule events are enabled by default.

This will create and attach a schedule event for the aggregate stateMachine which is disabled. If enabled it will call the aggregate stateMachine every 10 minutes.

stepFunctions:
  stateMachines:
    aggregate:
      events:
        - schedule:
            rate: rate(10 minutes)
            enabled: false
            input:
              key1: value1
              key2: value2
              stageParams:
                stage: dev
        - schedule:
            rate: cron(0 12 * * ? *)
            enabled: false
            inputPath: '$.stageVariables'

Specify Name and Description

Name and Description can be specified for a schedule event. These are not required properties.

events:
  - schedule:
      name: your-scheduled-rate-event-name
      description: 'your scheduled rate event description'
      rate: rate(2 hours)

Command

deploy

Runn sls deploy, the defined Stepfunctions are deployed.

invoke

$ sls invoke stepf --name <stepfunctionname> --data '{"foo":"bar"}'

options

--name or -n The name of the step function in your service that you want to invoke. Required.
--stage or -s The stage in your service you want to invoke your step function.
--region or -r The region in your stage that you want to invoke your step function.
--data or -d String data to be passed as an event to your step function.
--path or -p The path to a json file with input data to be passed to the invoked step function.

IAM Role

The IAM roles required to run Statemachine are automatically generated. It is also possible to specify ARN directly.