[EKS] [request]: enable graceful node shutdown

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**Tell us about your request**

EKS changelog (https://docs.aws.amazon.com/eks/latest/userguide/kubernetes-versions.html) seems to indicate tha graceful node shutdown is enabled on EKS 1.21. However, unless I’m mistaken, this is not the case. Could you consider enabling it?

**Which service(s) is this request for?**

EKS

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**

Without graceful node shutdown nor aws-node-termination-handler, an EKS cluster cannot take preventive actions in response to events which lead to instance shutdown (like ASG AZ rebalance, ASG instance refresh, spot instance preemption, etc). This can lead to service disruptions. Enabling graceful node shutdown would provide an out of the box solution.

**Are you currently working around this issue?**

No.

**Additional context**

ASG AZ rebalance can happen after a scale-down made by the cluster autoscaler.

Start with the EKS changelog linked in the issue and compare its statement about graceful node shutdown on EKS 1.21 with the reported behavior. Review how EKS handles ASG AZ rebalance, instance refresh, and Spot preemption, along with the aws-node-termination-handler workaround. Done means graceful node shutdown is enabled or the changelog and supported behavior clearly match.

Written by the indexing model from the issue text.