AWS Cloudformation : ECS Task definition ARN

Question

I have created cfn template to trigger cloudwatch event periodically to run an ecs task with Fargate launch type. The CW rule looks like below:

sfECSScheduleEventRule:
Type: AWS::Events::Rule
Description: ''
Properties:
  State: ENABLED
  ScheduleExpression: rate(1 minute)
  Name: !Sub sf-eventrule-ecs-${WPRegion}-${WPEnv}
  Targets:
  - Id: !Sub sf-ecs-target-task-${WPRegion}-${WPEnv}
    Arn: !GetAtt
      - ECSCluster
      - Arn
    RoleArn: !GetAtt
      - ECSTaskExecutionRole
      - Arn
    EcsParameters:
      #arn:aws:ecs:ap-northeast-1:448965722616:task-definition/fargate-task-jp-stg:latest
      TaskDefinitionArn: !Ref sfECSTaskDefinition          
      TaskCount: !Ref ECSTaskDesiredCount
      LaunchType: FARGATE
      PlatformVersion: 'LATEST'
      NetworkConfiguration:
        AwsVpcConfiguration:
          AssignPublicIp: DISABLED
          Subnets:
          - !Ref sfPrivateSubnet1

When I create the stack, I find the rule's target is like below:

Which fails to trigger the task. But when I change task revision from 4 to Latest manually , then it works. Task executes periodically.

How I can change the rule So that it points to the latest?

Answer 1

You are using:

TaskDefinitionArn: !Ref sfECSTaskDefinition 

According to the docs this returns arn with the revision number. Also according to TaskDefinitionArn :

If no task revision is supplied, it defaults to the most recent revision at the time of resource creation.

Thus I think if you manually create the arn, you should be able to get the most recent revision.

!Sub "arn:aws:ecs:${AWS::Region}:${AWS::AccountId}:task-definition/fargate-task-jp-stg"

Don't know if your task family name fargate-task-jp-stg is parameterized or not in the template. If yes, then you can also reference it in the Sub intrinsic function.