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

Adding a custom logical id for a stateMachine

You can use a custom logical id that is only unique within the stack as opposed to the name that needs to be unique globally. This can make referencing the state machine easier/simpler because you don’t have to duplicate the interpolation logic everywhere you reference the state machine.

service: messager

functions:
  sendMessage:
    handler: handler.sendMessage

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

plugins:
  - serverless-step-functions

You can then Ref: SendMessageStateMachine in various parts of CloudFormation or serverless.yml

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:

Share API Gateway and API Resources

You can share the same API Gateway between multiple projects by referencing its REST API ID and Root Resource ID in serverless.yml as follows:

service: service-name
provider:
  name: aws
  apiGateway:
    # REST API resource ID. Default is generated by the framework
    restApiId: xxxxxxxxxx
    # Root resource, represent as / path
    restApiRootResourceId: xxxxxxxxxx

functions:
  ...

If your application has many nested paths, you might also want to break them out into smaller services.

However, Cloudformation will throw an error if we try to generate an existing path resource. To avoid that, we reference the resource ID:

service: service-a
provider:
  apiGateway:
    restApiId: xxxxxxxxxx
    restApiRootResourceId: xxxxxxxxxx
    # List of existing resources that were created in the REST API. This is required or the stack will be conflicted
    restApiResources:
      /users: xxxxxxxxxx

functions:
  ...

Now we can define endpoints using existing API Gateway ressources

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

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. To enable the Access-Control-Max-Age preflight response header, set the maxAge property in the cors object:

stepFunctions:
  stateMachines:
    SfnApiGateway:
      events:
        - http:
            path: /playground/start
            method: post
            cors:
              origin: '*'
              maxAge: 86400

HTTP Endpoints with AWS_IAM Authorizers

If you want to require that the caller submit the IAM user’s access keys in order to be authenticated to invoke your Lambda Function, set the authorizer to AWS_IAM as shown in the following example:

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

HTTP Endpoints with Custom Authorizers

Custom Authorizers allow you to run an AWS Lambda Function before your targeted AWS Lambda Function. This is useful for Microservice Architectures or when you simply want to do some Authorization before running your business logic.

You can enable Custom Authorizers for your HTTP endpoint by setting the Authorizer in your http event to another function in the same service, as shown in the following example:

stepFunctions:
  stateMachines:
    hello:
      - http:
          path: posts/create
          method: post
          authorizer: authorizerFunc
      definition:

If the Authorizer function does not exist in your service but exists in AWS, you can provide the ARN of the Lambda function instead of the function name, as shown in the following example:

stepFunctions:
  stateMachines:
    hello:
      - http:
          path: posts/create
          method: post
          authorizer: xxx:xxx:Lambda-Name
      definition:

Share Authorizer

Auto-created Authorizer is convenient for conventional setup. However, when you need to define your custom Authorizer, or use COGNITO_USER_POOLS authorizer with shared API Gateway, it is painful because of AWS limitation. Sharing Authorizer is a better way to do.

stepFunctions:
  stateMachines:
    createUser:
      ...
      events:
        - http:
            path: /users
            ...     
            authorizer:
              # Provide both type and authorizerId
              type: COGNITO_USER_POOLS # TOKEN, CUSTOM or COGNITO_USER_POOLS, same as AWS Cloudformation documentation
              authorizerId: 
                Ref: ApiGatewayAuthorizer  # or hard-code Authorizer ID

Customizing request body mapping templates

The plugin generates default body mapping templates for application/json and application/x-www-form-urlencoded content types. If you’d like to add more content types or customize the default ones, you can do so by including them in serverless.yml:

stepFunctions:
  stateMachines:
    hello:
      events:
        - http:
            path: posts/create
            method: POST
            request:
              template:
                application/json: |
                  #set( $body = $util.escapeJavaScript($input.json('$')) )
                  #set( $name = $util.escapeJavaScript($input.json('$.data.attributes.order_id')) )
                  {
                    "input": "$body",
                    "name": "$name",
                    "stateMachineArn":"arn:aws:states:#{AWS::Region}:#{AWS::AccountId}:stateMachine:processOrderFlow-${opt:stage}"
                  }
      name: processOrderFlow-${opt:stage}
      definition:

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

Run 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