aws-cdk-lib.aws-autoscaling: Add support for configuring AutoScalingGroup's instance maintenance policy

[kirksaunders]

Describe the feature

AWS EC2 AutoScaling just added a new way to manage the replacement of instances, called the Instance Maintenance Policy (launch announcement). The policy allows you to control the percentage of instances above and below your desired capacity to allow during replacements/updates. And in particular, this policy now allows a "Launch-Before-Terminate" strategy, to perform replacements without impacting ASG healthy capacity.

Use Case

My team wants to use the new "Launch-Before-Terminate" feature to more safely update our ASGs. In particular, we have a few fleets with very few instances. To safely update now, we must overscale our fleets to maintain enough capacity for serving requests. With this new feature, we can keep our fleets descaled, and use the "Launch-Before-Terminate" feature to safely update.

Proposed Solution

Add a new property to the AutoScaling construct that allows you to set the instance maintenance policy.

Other Information

References for the policy:
[1] https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-autoscaling-autoscalinggroup-instancemaintenancepolicy.html
[2] https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-autoscaling-autoscalinggroup.html
[3] https://docs.aws.amazon.com/autoscaling/ec2/userguide/ec2-auto-scaling-instance-maintenance-policy.html
[4] https://docs.aws.amazon.com/autoscaling/ec2/userguide/set-instance-maintenance-policy-on-group.html
[5] https://aws.amazon.com/blogs/compute/introducing-instance-maintenance-policy-for-amazon-ec2-auto-scaling/

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

CDK version used

v2.109.0

Environment details (OS name and version, etc.)

Amazon Linux 2

[pahud]

Yes we welcome pull requests from the community for this feature. Before that, as CFN has supported it, we can use escape hatches to add property overrides as a workaround.

[go-to-k]

I will take this.

[github-actions]

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[abhishek-parative]

@go-to-k @pahud Is there a way to set the "Launch Before Terminate" setting via CDK? I looked through the attached PR and it only modifies the Min and Max health percentage.

[go-to-k]

@abhishek-parative

Yes, the "Launch Before Terminate" policy is equal to a setting with the Min = 100% (and the Max > 100%). So this setting allows the policy to be used in the CDK.