Cloudformation: ELB listener rule creation fails with "Invalid request provided"

Question

I'm trying to stand up a small Cloudformation stack comprised of an application load balancer, a target group, and an ECS service. However, the stack fails to create the WidgetsServiceLbListenerRule resource with the following error:

"Invalid request provided: AWS::ElasticLoadBalancingV2::ListenerRule Validation exception" (RequestToken: 98057bbb-ad4f-5f09-3e89-cc6b645c6e7f, HandlerErrorCode: InvalidRequest)

Why is the listener rule failing to create?

Here's the relevant stack code:

Resources:

  # The load balancer
  Lb:
    Type: AWS::ElasticLoadBalancingV2::LoadBalancer
    Properties:
      Name: !Join ['', [!Ref Env, '-rest-api-lb-rev', !Ref Rev]]
      Scheme: internet-facing
      SecurityGroups:
        - !Ref LbSg
      Subnets:
        - Fn::ImportValue: !Sub "${VpcStackName}-PubSubnet1Id"
        - Fn::ImportValue: !Sub "${VpcStackName}-PubSubnet2Id"
        - Fn::ImportValue: !Sub "${VpcStackName}-PubSubnet3Id"
      Type: application
  LbListener:
    Type: AWS::ElasticLoadBalancingV2::Listener
    Properties:
      DefaultActions:
        - Type: fixed-response
          FixedResponseConfig:
            ContentType: text/plain
            MessageBody: The specified route doesn't exist
            StatusCode: 404
      LoadBalancerArn: !Ref Lb
      Port: 80
      Protocol: HTTP

  # Widgets service
  WidgetsServiceLbTargetGroup:
    Type: AWS::ElasticLoadBalancingV2::TargetGroup
    Properties:
      HealthCheckPath: /actuator/health
      Name: !Join ['', [!Ref Env, '-widgets-rev', !Ref Rev]]
      Port: 80
      Protocol: HTTP
      VpcId:
        Fn::ImportValue: !Sub "${VpcStackName}-VpcId"

  # THIS ONE FAILS TO CREATE
  WidgetsServiceLbListenerRule:
    Type: AWS::ElasticLoadBalancingV2::ListenerRule
    Properties:
      Actions:
        - Type: forward
          TargetGroupArn: !Ref WidgetsServiceLbTargetGroup
      Conditions:
        - Field: path-pattern
          Values:
            - '/widgets*'
      ListenerArn: Ref !LbListener
      Priority: 1
 
<ECS service and other assets omitted for brevity>

More info

• We have several existing stacks in our AWS account that use almost the exact same code. There aren't any meaningful differences between those and this one, and they work fine.
• I created a stack without the WidgetsServiceLbListenerRule and then tried to add it back in as a change set. This also produced the same error.
• I was able to successfully create the rule using the following AWS CLI command: aws --profile clexp elbv2 create-rule --listener-arn <arn> --priority 1 --conditions file://conditions.json --actions file://actions.json

conditions.json:

[{"Type": "forward","TargetGroupArn": "<arn>"}]

actions.json:

[{"Field": "path-pattern","Values": ["/widgets*"]}]

Any help is much appreciated.

Answer 1

Instead of :

ListenerArn: Ref !LbListener

it should be:

ListenerArn: !Ref LbListener