Serverless Step Functions

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serverless Build Status npm version Coverage Status MIT License

Serverless Step Functions

Serverless 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.

custom:
  accountId: xxxxxxxx

functions:
  hellofunc:
    handler: handler.hello

stepFunctions:
  stateMachines:
    hellostepfunc1:
      events:
        - http:
            path: gofunction
            method: GET
      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:${opt:region}:${self:custom.accountId}:function:${self:service}-${opt:stage}-hello
            End: true
    hellostepfunc2:
      definition:
        StartAt: HelloWorld2
        States:
          HelloWorld2:
            Type: Task
            Resource: arn:aws:states:${opt:region}:${self:custom.accountId}:activity:myTask
            End: true
  activities:
    - myTask
    - yourTask

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

Please note, that during normalization some characters will be changed to adhere to CloudFormation templates. You can get the real statemachine name using { "Fn::GetAtt": ["MyStateMachine", "Name"] }.

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"}'

Command

deploy

Runn sls deploy, the defined Stepfunctions are deployed.

invoke

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

options

IAM Role

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

Here’s an example:

stepFunctions:
  stateMachines:
    hello:
      role: arn:aws:iam::xxxxxxxx:role/yourRole
      definition:

Tips

How to specify the stateMachine ARN to environment variables

Here is serverless.yml sample to specify the stateMachine ARN to environment variables. This makes it possible to trigger your statemachine through Lambda events

functions:
  hello:
    handler: handler.hello
    environment:
      statemachine_arn: ${self:resources.Outputs.MyStateMachine.Value}

stepFunctions:
  stateMachines:
    hellostepfunc:
      name: myStateMachine
      definition:
        <your definition>

resources:
  Outputs:
    MyStateMachine:
      Description: The ARN of the example state machine
      Value:
        Ref: MyStateMachine

plugins:
  - serverless-step-functions

Sample statemachines setting in serverless.yml

Wait State

custom:
  accountId: <Here is your accountId>

functions:
  hello:
    handler: handler.hello

stepFunctions:
  stateMachines:
    yourWateMachine:
      definition:
        Comment: "An example of the Amazon States Language using wait states"
        StartAt: FirstState
        States:
          FirstState:
            Type: Task
            Resource: arn:aws:lambda:${opt:region}:${self:custom.accountId}:function:${self:service}-${opt:stage}-hello
            Next: wait_using_seconds
          wait_using_seconds:
            Type: Wait
            Seconds: 10
            Next: wait_using_timestamp
          wait_using_timestamp:
            Type: Wait
            Timestamp: '2015-09-04T01:59:00Z'
            Next: wait_using_timestamp_path
          wait_using_timestamp_path:
            Type: Wait
            TimestampPath: "$.expirydate"
            Next: wait_using_seconds_path
          wait_using_seconds_path:
            Type: Wait
            SecondsPath: "$.expiryseconds"
            Next: FinalState
          FinalState:
            Type: Task
            Resource: arn:aws:lambda:${opt:region}:${self:custom.accountId}:function:${self:service}-${opt:stage}-hello
            End: true

Retry Failture

custom:
  accountId: <Here is your accountId>

functions:
  hello:
    handler: handler.hello

stepFunctions:
  stateMachines:
    yourRetryMachine:
      definition:
        Comment: "A Retry example of the Amazon States Language using an AWS Lambda Function"
        StartAt: HelloWorld
        States:
          HelloWorld:
            Type: Task
            Resource: arn:aws:lambda:${opt:region}:${self:custom.accountId}:function:${self:service}-${opt:stage}-hello
            Retry:
            - ErrorEquals:
              - HandledError
              IntervalSeconds: 1
              MaxAttempts: 2
              BackoffRate: 2
            - ErrorEquals:
              - States.TaskFailed
              IntervalSeconds: 30
              MaxAttempts: 2
              BackoffRate: 2
            - ErrorEquals:
              - States.ALL
              IntervalSeconds: 5
              MaxAttempts: 5
              BackoffRate: 2
            End: true

Parallel

custom:
  accountId: <Here is your accountId>

functions:
  hello:
    handler: handler.hello

stepFunctions:
  stateMachines:
    yourParallelMachine:
      definition:
        Comment: "An example of the Amazon States Language using a parallel state to execute two branches at the same time."
        StartAt: Parallel
        States:
          Parallel:
            Type: Parallel
            Next: Final State
            Branches:
            - StartAt: Wait 20s
              States:
                Wait 20s:
                  Type: Wait
                  Seconds: 20
                  End: true
            - StartAt: Pass
              States:
                Pass:
                  Type: Pass
                  Next: Wait 10s
                Wait 10s:
                  Type: Wait
                  Seconds: 10
                  End: true
          Final State:
            Type: Pass
            End: true

Catch Failure

custom:
  accountId: <Here is your accountId>

functions:
  hello:
    handler: handler.hello

stepFunctions:
  stateMachines:
    yourCatchMachine:
      definition:
        Comment: "A Catch example of the Amazon States Language using an AWS Lambda Function"
        StartAt: HelloWorld
        States:
          HelloWorld:
            Type: Task
            Resource: arn:aws:lambda:${opt:region}:${self:custom.accountId}:function:${self:service}-${opt:stage}-hello
            Catch:
            - ErrorEquals:
              - HandledError
              Next: CustomErrorFallback
            - ErrorEquals:
              - States.TaskFailed
              Next: ReservedTypeFallback
            - ErrorEquals:
              - States.ALL
              Next: CatchAllFallback
            End: true
          CustomErrorFallback:
            Type: Pass
            Result: "This is a fallback from a custom lambda function exception"
            End: true
          ReservedTypeFallback:
            Type: Pass
            Result: "This is a fallback from a reserved error code"
            End: true
          CatchAllFallback:
            Type: Pass
            Result: "This is a fallback from a reserved error code"
            End: true

Choice

custom:
  accountId: <Here is your account Id>

functions:
  hello1:
    handler: handler.hello1
  hello2:
    handler: handler.hello2
  hello3:
    handler: handler.hello3
  hello4:
    handler: handler.hello4

stepFunctions:
  stateMachines:
    yourChoiceMachine:
      definition:
        Comment: "An example of the Amazon States Language using a choice state."
        StartAt: FirstState
        States:
          FirstState:
            Type: Task
            Resource: arn:aws:lambda:${opt:region}:${self:custom.accountId}:function:${self:service}-${opt:stage}-hello1
            Next: ChoiceState
          ChoiceState:
            Type: Choice
            Choices:
            - Variable: "$.foo"
              NumericEquals: 1
              Next: FirstMatchState
            - Variable: "$.foo"
              NumericEquals: 2
              Next: SecondMatchState
            Default: DefaultState
          FirstMatchState:
            Type: Task
            Resource: arn:aws:lambda:${opt:region}:${self:custom.accountId}:function:${self:service}-${opt:stage}-hello2
            Next: NextState
          SecondMatchState:
            Type: Task
            Resource: arn:aws:lambda:${opt:region}:${self:custom.accountId}:function:${self:service}-${opt:stage}-hello3
            Next: NextState
          DefaultState:
            Type: Fail
            Cause: "No Matches!"
          NextState:
            Type: Task
            Resource: arn:aws:lambda:${opt:region}:${self:custom.accountId}:function:${self:service}-${opt:stage}-hello4
            End: true