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Fix/aws asg unsafe decommission 5829 #6818

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Fix/aws asg unsafe decommission 5829 #6818

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ruiscosta
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Merge branch 'fix/aws-asg-placeholder-decommission'

This merge resolves an issue in the Kubernetes Cluster Autoscaler where actual instances within AWS Auto Scaling Groups (ASGs) were incorrectly decommissioned instead of placeholders. The updates ensure that placeholders are exclusively targeted for scaling down under conditions where recent scaling activities have failed. This prevents the accidental termination of active nodes and enhances the reliability of the autoscaler in AWS environments.

Key improvements include:

  • Refined logic to strictly identify unsuccessful scaling activities.
  • Ensured that scaling operations affect placeholders only, preventing unintended impacts on real instances.
  • Expanded unit tests and validations to bolster the resilience and correctness of the scaling process.

Fixes #5829

What type of PR is this?

/kind bug

What this PR does / why we need it:

This PR prevents the Kubernetes Cluster Autoscaler from erroneously decommissioning actual nodes during scale-down operations in AWS environments, which could lead to unintended service disruptions.

Which issue(s) this PR fixes:

Fixes #5829

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Fix an issue in the Kubernetes Cluster Autoscaler where actual AWS instances could be incorrectly scaled down instead of placeholders.

This merge resolves the issue where the Kubernetes Cluster Autoscaler incorrectly decommissions actual instances instead of placeholders within AWS ASGs. The fix ensures that only placeholders are considered for scaling down when recent scaling activities fail, thereby preventing the accidental removal of active nodes. Enhanced unit tests and checks are included to ensure robustness.

Fixes #5829
This merge resolves the issue where the Kubernetes Cluster Autoscaler incorrectly decommissions actual instances instead of placeholders within AWS ASGs. The fix ensures that only placeholders are considered for scaling down when recent scaling activities fail, thereby preventing the accidental removal of active nodes. Enhanced unit tests and checks are included to ensure robustness.

Fixes #5829
@k8s-ci-robot k8s-ci-robot added kind/bug Categorizes issue or PR as related to a bug. do-not-merge/invalid-commit-message Indicates that a PR should not merge because it has an invalid commit message. labels May 10, 2024
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Keywords which can automatically close issues and at(@) or hashtag(#) mentions are not allowed in commit messages.

The list of commits with invalid commit messages:

  • fb69323 fix: Handle placeholder instance decommission safely in AWS ASGs
  • 9dfbb4d fix: Handle placeholder instance decommission safely in AWS ASGs

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linux-foundation-easycla bot commented May 10, 2024

CLA Not Signed

@k8s-ci-robot k8s-ci-robot added cncf-cla: no Indicates the PR's author has not signed the CNCF CLA. needs-ok-to-test Indicates a PR that requires an org member to verify it is safe to test. labels May 10, 2024
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Hi @ruiscosta. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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@k8s-ci-robot k8s-ci-robot added the size/L Denotes a PR that changes 100-499 lines, ignoring generated files. label May 10, 2024
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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: ruiscosta
Once this PR has been reviewed and has the lgtm label, please assign drmorr0 for approval. For more information see the Kubernetes Code Review Process.

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@k8s-ci-robot k8s-ci-robot requested a review from drmorr0 May 10, 2024 19:33
@k8s-ci-robot k8s-ci-robot added the area/provider/aws Issues or PRs related to aws provider label May 10, 2024
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/ok-to-test

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@aaroniscode: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

In response to this:

/ok-to-test

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klog.V(4).Infof("instance %s is detected as a placeholder, decreasing ASG requested size instead "+
"of deleting instance", instance.Name)
m.decreaseAsgSizeByOneNoLock(commonAsg)
if !recentScalingActivitySuccess {
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Hi @ruiscosta I don't believe this actually solves the problem. Consider the following scenario:

  1. We scale up the ASG by 10 instances. AWS creates 3 of them, and then fails on the remaining 7.
  2. DeleteInstances is called with those 10 instances; 7 of them are placeholders
  3. In lines 321 we check to see if the most recent scaling activity was successful or not, which returns false since 7 instances could not be created.
  4. Now for each instance in the loop, we decrease the ASG size by one, which reduces the ASG size by 7.
  5. In between the check in line 321 and (say) the 5th iteration of the loop, AWS launches a new instance, which joins the cluster. Our information about what instances are actually placeholders is now out of date, and we get the same problem that we had before.

We "could" check the recent scaling activity in every iteration of the loop, at the expense of making a lot more API calls, which I think is undesirable, and is still subject to a race between when you make the check and when you change the ASG size.

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dims commented May 24, 2024

/ok-to-test

@k8s-ci-robot k8s-ci-robot added ok-to-test Indicates a non-member PR verified by an org member that is safe to test. and removed needs-ok-to-test Indicates a PR that requires an org member to verify it is safe to test. labels May 24, 2024
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dims commented May 25, 2024

/easycla

ravisinha0506 added a commit to ravisinha0506/autoscaler that referenced this pull request Jun 7, 2024
This merge resolves an issue in the Kubernetes Cluster Autoscaler where actual instances within AWS Auto Scaling Groups (ASGs) were incorrectly decommissioned instead of placeholders. The updates ensure that placeholders are exclusively targeted for scaling down under conditions where recent scaling activities have failed. This prevents the accidental termination of active nodes and enhances the reliability of the autoscaler in AWS environments.

Fixes kubernetes#5829
ravisinha0506 added a commit to ravisinha0506/autoscaler that referenced this pull request Jun 10, 2024
This change expands on pr kubernetes#6818

This merge resolves an issue in the Kubernetes Cluster Autoscaler where actual instances within AWS Auto Scaling Groups (ASGs) were incorrectly decommissioned instead of placeholders. The updates ensure that placeholders are exclusively targeted for scaling down under conditions where recent scaling activities have failed. This prevents the accidental termination of active nodes and enhances the reliability of the autoscaler in AWS environments.

Fixes kubernetes#5829
@ruiscosta ruiscosta closed this Jun 12, 2024
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[AWS] Unsafe decomissioning of nodes when ASGs are out of instances
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