Serverless Step Functions

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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.

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

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

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:#{AWS::Region}:#{AWS::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:#{AWS::Region}:#{AWS::AccountId}:function:${self:service}-${opt:stage}-hello
            End: true
plugins:
  - serverless-step-functions
  - serverless-pseudo-parameters

Retry Failture

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:#{AWS::Region}:#{AWS::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
plugins:
  - serverless-step-functions
  - serverless-pseudo-parameters

Parallel

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

Catch Failure

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:#{AWS::Region}:#{AWS::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
plugins:
  - serverless-step-functions
  - serverless-pseudo-parameters

Choice

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:#{AWS::Region}:#{AWS::AccountId}:function:${self:service}-${opt:stage}-hello2
            Next: NextState
          SecondMatchState:
            Type: Task
            Resource: arn:aws:lambda:#{AWS::Region}:#{AWS::AccountId}:function:${self:service}-${opt:stage}-hello3
            Next: NextState
          DefaultState:
            Type: Fail
            Cause: "No Matches!"
          NextState:
            Type: Task
            Resource: arn:aws:lambda:#{AWS::Region}:#{AWS::AccountId}:function:${self:service}-${opt:stage}-hello4
            End: true
plugins:
  - serverless-step-functions
  - serverless-pseudo-parameters