Troubleshooting AutoScalingPolicy creation with AWS CloudFormation

Question

When creating an AutoScalingGroup with attached AutoScalingPolicy in AWS using CloudFormation, you might get the error

the load balancer does not route traffic to the target group

The same CloudFormation script works well if the AutoScalingPolicy is excluded from the script. Also, using the ResourceLable as Output of the script without the AutoScalingPolicy, the output looks correct.

Assumption: there is an unresolved dependency between the AutoScalingPolicy and the LoadBalancer or the corresponding TargetGroup.

Answer 1

To ensure the dependencies are correctly resolved and the LoadBalancer as well as the TargetGroup are being created prior to the creation of the AutoScalingPolicy, use the DependsOn attribute in the AutoScalingPolicy, referencing the ELBListener:

myAutoScalingPolicy:
  Type: AWS::AutoScaling::ScalingPolicy
  DependsOn: myElbListener
  Properties:
    AutoScalingGroupName: !Ref myAutoScalingGroup
    PolicyType: TargetTrackingScaling
    TargetTrackingConfiguration:
      PredefinedMetricSpecification:
        PredefinedMetricType: ALBRequestCountPerTarget
        ResourceLabel: !Join 
          - '/' 
          - - !GetAtt myELB.LoadBalancerFullName
            - !GetAtt myELBTargetGroup.TargetGroupFullName
      TargetValue: '50'