AWSTemplateFormatVersion: 2010-09-09
Transform: AWS::Serverless-2016-10-31
Description: Serverless patterns - EventBridge to Step Functions

Resources:

  # CloudWatch Log Group
  EC2StateWatcherLogs:
    Type: AWS::Logs::LogGroup

  # Step Function
  EC2StateWatcher:
    Type: AWS::Serverless::StateMachine
    Properties:
      # Logging is a good idea. We also need at least one policy attached to the Step
      # Function in order to deploy.
      Logging:
        Level: ERROR
        Destinations:
          - CloudWatchLogsLogGroup:
              LogGroupArn: !GetAtt EC2StateWatcherLogs.Arn
      Policies:
        - Statement:
          - Effect: Allow
            Action:
              - logs:*
            Resource: "*"
      Definition:
        StartAt: What Happened?
        States:
          # The three states that trigger this Step Function each have their own path.
          What Happened?:
            Type: Choice
            Choices:
              - Variable: $.state
                StringEquals: running
                Next: It's Running
              - Variable: $.state
                StringEquals: stopped
                Next: It's Stopped
              - Variable: $.state
                StringEquals: terminated
                Next: It's Gone
          # These Pass states can be replaced to contain business logic for reacting to
          # state changes. See other Step Function to Service patterns for examples.
          It's Running:
            Type: Pass
            End: true
          It's Stopped:
            Type: Pass
            End: true
          It's Gone:
            Type: Pass
            End: true
      Events:
        StateChange:
          Type: EventBridgeRule
          Properties:
            EventBusName: default
            # The detail key contains the EC2 specific event data. In this example, the
            # rest of the event properties are not needed and discarded.
            InputPath: $.detail
            Pattern:
              source:
                - aws.ec2
              detail:
                state:
                  - running
                  - stopped
                  - terminated

Outputs:

  EC2StateWatcherArn:
    Description: EC2StateWatcher state machine ARN
    Value: !Ref EC2StateWatcher