✨ feat: Implement autoscaling from zero by auto-populating AWSMachineTemplate capacity #5711

LiangquanLi930 · 2025-10-15T18:37:11Z

✨ Implement autoscaling from zero by auto-populating AWSMachineTemplate capacity

What type of PR is this?
/kind feature

What this PR does / why we need it:
This PR implements the Cluster API autoscaling from zero proposal for CAPA by adding a controller that automatically populates AWSMachineTemplate.Status.Capacity with instance type information.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Special notes for your reviewer:

Checklist:

Release note:

Implement autoscaling from zero by auto-populating AWSMachineTemplate capacity

k8s-ci-robot · 2025-10-15T18:37:18Z

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k8s-ci-robot · 2025-10-15T18:37:20Z

Hi @LiangquanLi930. Thanks for your PR.

I'm waiting for a kubernetes-sigs 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.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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elmiko · 2025-10-15T18:47:47Z

/ok-to-test

LiangquanLi930 · 2025-10-20T09:20:55Z

/test pull-cluster-api-provider-aws-e2e-blocking

chrischdi · 2025-10-22T08:10:59Z

controllers/awsmachinetemplate_controller.go

+	if len(awsMachineTemplate.Status.Capacity) > 0 {
+		return ctrl.Result{}, nil
+	}


What if the capacity is not correct? Or is the .spec.template.spec.instanceType immutable?

IIUC, spec.template.spec.instanceType is immutable:

cluster-api-provider-aws/api/v1beta2/awsmachinetemplate_webhook.go

Lines 230 to 240 in 427f450

if !topology.ShouldSkipImmutabilityChecks(req, newAWSMachineTemplate) && !cmp.Equal(newAWSMachineTemplate.Spec, oldAWSMachineTemplate.Spec) {

if oldAWSMachineTemplate.Spec.Template.Spec.InstanceMetadataOptions == nil {

oldAWSMachineTemplate.Spec.Template.Spec.InstanceMetadataOptions = newAWSMachineTemplate.Spec.Template.Spec.InstanceMetadataOptions

}

if !cmp.Equal(newAWSMachineTemplate.Spec.Template.Spec, oldAWSMachineTemplate.Spec.Template.Spec) {

allErrs = append(allErrs,

field.Invalid(field.NewPath("spec", "template", "spec"), newAWSMachineTemplate, "AWSMachineTemplate.Spec is immutable"),

)

}

}

The webhook enforces that spec.template.spec cannot be changed after creation, except when topology.ShouldSkipImmutabilityChecks() returns true (which is only for ClusterClass topology patches).

Therefore, I think the current early-return logic is correct.

Sounds good

chrischdi · 2025-10-22T08:16:32Z

controllers/awsmachinetemplate_controller_unit_test.go

+	clusterv1 "sigs.k8s.io/cluster-api/api/v1beta1"
+)
+
+func TestAWSMachineTemplateReconciler(t *testing.T) {


Could there also be a unit test which expects actual correct values instead of just checking "capacity" is set?

chrischdi

Should this also add the nodeInfo information as described in https://github.com/kubernetes-sigs/cluster-api/blob/main/docs/proposals/20210310-opt-in-autoscaling-from-zero.md ?

elmiko · 2025-10-22T13:27:51Z

nodeInfo would be nice to have, architecture should be relatively easy to determine but i'm not sure about operating system.

that said, nodeInfo is an extension to the original opt-in scale from zero, if arch and o/s are not present the autoscaler will still be able to scale based on resources alone.

LiangquanLi930 · 2025-10-22T17:00:48Z

/test pull-cluster-api-provider-aws-e2e

elmiko

in general this is looking good to me, i tend to agree with Christian's questions.

LiangquanLi930 · 2025-10-23T06:53:05Z

/test pull-cluster-api-provider-aws-e2e

LiangquanLi930 · 2025-10-23T10:34:46Z

/test pull-cluster-api-provider-aws-e2e

… capacity

LiangquanLi930 · 2025-10-24T04:08:08Z

/test pull-cluster-api-provider-aws-test

k8s-ci-robot · 2025-10-28T07:13:16Z

@LiangquanLi930: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-cluster-api-provider-aws-e2e	`3208d4c`	link	false	`/test pull-cluster-api-provider-aws-e2e`

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository. I understand the commands that are listed here.

LiangquanLi930 · 2025-10-29T06:25:32Z

/test pull-cluster-api-provider-aws-e2e

k8s-ci-robot added kind/feature Categorizes issue or PR as related to a new feature. do-not-merge/release-note-label-needed Indicates that a PR should not merge because it's missing one of the release note labels. cncf-cla: yes Indicates the PR's author has signed the CNCF CLA. labels Oct 15, 2025

k8s-ci-robot added the needs-priority label Oct 15, 2025

k8s-ci-robot requested review from AndiDog and cnmcavoy October 15, 2025 18:37

k8s-ci-robot added needs-ok-to-test Indicates a PR that requires an org member to verify it is safe to test. size/L Denotes a PR that changes 100-499 lines, ignoring generated files. labels Oct 15, 2025

LiangquanLi930 changed the title ~~✨ Implement autoscaling from zero by auto-populating AWSMachineTemplate capacity~~ WIP ✨ Implement autoscaling from zero by auto-populating AWSMachineTemplate capacity Oct 15, 2025

k8s-ci-robot added the do-not-merge/work-in-progress Indicates that a PR should not merge because it is a work in progress. label Oct 15, 2025

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 Oct 15, 2025

LiangquanLi930 force-pushed the opt-in-autoscaling-from-zero branch 6 times, most recently from 50f8188 to f1ee365 Compare October 20, 2025 08:39

LiangquanLi930 force-pushed the opt-in-autoscaling-from-zero branch from f1ee365 to 3be8f4d Compare October 20, 2025 11:21

k8s-ci-robot added size/XL Denotes a PR that changes 500-999 lines, ignoring generated files. and removed size/L Denotes a PR that changes 100-499 lines, ignoring generated files. labels Oct 20, 2025

LiangquanLi930 force-pushed the opt-in-autoscaling-from-zero branch 2 times, most recently from 01be987 to 915f55b Compare October 20, 2025 12:57

k8s-ci-robot added size/L Denotes a PR that changes 100-499 lines, ignoring generated files. and removed size/XL Denotes a PR that changes 500-999 lines, ignoring generated files. labels Oct 20, 2025

LiangquanLi930 force-pushed the opt-in-autoscaling-from-zero branch from 915f55b to b3850d1 Compare October 20, 2025 14:42

k8s-ci-robot assigned elmiko Oct 21, 2025

chrischdi reviewed Oct 22, 2025

View reviewed changes

elmiko reviewed Oct 22, 2025

View reviewed changes

LiangquanLi930 force-pushed the opt-in-autoscaling-from-zero branch from 679c53a to 3208d4c Compare October 23, 2025 09:51

Implement autoscaling from zero by auto-populating AWSMachineTemplate…

5abc575

… capacity

LiangquanLi930 force-pushed the opt-in-autoscaling-from-zero branch 2 times, most recently from f02a539 to cee9b2e Compare October 23, 2025 18:44

LiangquanLi930 force-pushed the opt-in-autoscaling-from-zero branch 11 times, most recently from d87e524 to ae396bf Compare October 28, 2025 06:56

add AWSMachineTemplate NodeInfo

15d3232

LiangquanLi930 force-pushed the opt-in-autoscaling-from-zero branch from ae396bf to 15d3232 Compare October 28, 2025 09:11

test

ded149b

	if !topology.ShouldSkipImmutabilityChecks(req, newAWSMachineTemplate) && !cmp.Equal(newAWSMachineTemplate.Spec, oldAWSMachineTemplate.Spec) {
	if oldAWSMachineTemplate.Spec.Template.Spec.InstanceMetadataOptions == nil {
	oldAWSMachineTemplate.Spec.Template.Spec.InstanceMetadataOptions = newAWSMachineTemplate.Spec.Template.Spec.InstanceMetadataOptions
	}

	if !cmp.Equal(newAWSMachineTemplate.Spec.Template.Spec, oldAWSMachineTemplate.Spec.Template.Spec) {
	allErrs = append(allErrs,
	field.Invalid(field.NewPath("spec", "template", "spec"), newAWSMachineTemplate, "AWSMachineTemplate.Spec is immutable"),
	)
	}
	}

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✨ feat: Implement autoscaling from zero by auto-populating AWSMachineTemplate capacity #5711

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✨ feat: Implement autoscaling from zero by auto-populating AWSMachineTemplate capacity #5711

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