Use CloudFormation for Auto Scaling policies - Amazon ElastiCache
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Use CloudFormation for Auto Scaling policies

This snippet shows how to create a target tracking policy and apply it to an AWS::ElastiCache::ReplicationGroup resource using the AWS::ApplicationAutoScaling::ScalableTarget resource. It uses the Fn::Join and Ref intrinsic functions to construct the ResourceId property with the logical name of the AWS::ElastiCache::ReplicationGroup resource that is specified in the same template. 

ScalingTarget:
   Type: 'AWS::ApplicationAutoScaling::ScalableTarget'
   Properties:
     MaxCapacity: 3
     MinCapacity: 1
     ResourceId: !Sub replication-group/${logicalName}
     ScalableDimension: 'elasticache:replication-group:NodeGroups'
     ServiceNamespace: elasticache
     RoleARN: !Sub "arn:aws:iam::${AWS::AccountId}:role/aws-service-role/elasticache.application-autoscaling.amazonaws.com/AWSServiceRoleForApplicationAutoScaling_ElastiCacheRG"

  ScalingPolicy:
    Type: "AWS::ApplicationAutoScaling::ScalingPolicy"
    Properties:
      ScalingTargetId: !Ref ScalingTarget
      ServiceNamespace: elasticache
      PolicyName: testpolicy
      PolicyType: TargetTrackingScaling
      ScalableDimension: 'elasticache:replication-group:NodeGroups'
      TargetTrackingScalingPolicyConfiguration:
        PredefinedMetricSpecification:
          PredefinedMetricType: ElastiCachePrimaryEngineCPUUtilization
        TargetValue: 40