aws-autoscaling: Step scaling properties expose unsupported cooldown property

[lucajone]

Describe the bug

The StepScalingPolicyProps interface and related StepScalingActionProps interface expose a cooldown property, which if specified becomes the cooldown property of a CfnScalingPolicy here:

aws-cdk/packages/aws-cdk-lib/aws-autoscaling/lib/step-scaling-action.ts

Line 77 in a7b4e29

cooldown: props.cooldown && props.cooldown.toSeconds().toString(),

However, cooldown is not a supported property for step scaling policies. The documentation for the AWS::AutoScaling::ScalingPolicy resource says:

Valid only if the policy type is SimpleScaling. For more information, see Scaling cooldowns for Amazon EC2 Auto Scaling in the Amazon EC2 Auto Scaling User Guide.

Specifying this property has no effect and can cause CloudFormation deployment errors in some regions (such as ap-southeast-4).

Expected Behavior

Since this property has no effect and can cause deployment errors, it should not be possible to specify for step scaling policies and should be deprecated.

Current Behavior

The property can be specified and results in an AWS::AutoScaling::ScalingPolicy with PolicyType set to StepScaling and the Cooldown property present. This is ineffectual or can cause the following error on deployment, depending on the region:

Property Cooldown cannot be specified.

Reproduction Steps

The following application reproduces the deployment error when deployed to ap-southeast-4.

import { App, Duration, Stack, StackProps } from 'aws-cdk-lib';
import { AutoScalingGroup, } from 'aws-cdk-lib/aws-autoscaling';
import { AmazonLinuxCpuType, InstanceClass, InstanceSize, InstanceType, MachineImage, Vpc } from 'aws-cdk-lib/aws-ec2';
import { Construct } from 'constructs';
import { Metric } from 'aws-cdk-lib/aws-cloudwatch';

export class ReproStack extends Stack {
  constructor(scope: Construct, id: string, props?: StackProps) {
    super(scope, id, props);

    const vpc = new Vpc(this, "VPC");
    const asg = new AutoScalingGroup(this, "ASG", {
      vpc,
      machineImage: MachineImage.latestAmazonLinux2023({ cpuType: AmazonLinuxCpuType.ARM_64 }),
      instanceType: InstanceType.of(InstanceClass.T4G, InstanceSize.MICRO),
    });

    const metric = new Metric({
      namespace: "Repro",
      metricName: "Metric",
    });

    asg.scaleOnMetric("MetricScale", {
      metric,
      scalingSteps: [
        { upper: 10, change: -5 },
        { lower: 50, change: 5 }
      ],
      cooldown: Duration.minutes(5),
    })
  }
}

const app = new App();
new ReproStack(app, "Repro");

Possible Solution

No response

Additional Information/Context

No response

CDK CLI Version

2.136.1

Framework Version

No response

Node.js Version

v18.0.0

OS

macOS

Language

TypeScript

Language Version

5.4.3

Other information

(Amazon ticket D120666119 has some more detail.)

[khushail]

Hi @lucajone thanks for reporting this. I implemented this in us-east-1 and it succeeded. I wonder though it would have any impact. You are absolutely right in saying exposing this property as multiple interfaces won't serve the purpose as its exclusively for 'SimpleScaling` policy type.

Marking it as appropriate.

[github-actions]

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