WIP : [release-4.20] kubelet-config compressible patch

[ngopalak-redhat]

- What I did

• Added compressible kubelet MachineConfig creation at controller startup using the templated kubelet configuration
• Implemented ensureCompressibleMachineConfigs() to create 50--compressible-kubelet-override MachineConfigs for all pools
• Added waitForTemplateGeneration() to ensure ControllerConfig is reconciled before creating compressible MachineConfigs
• Created bootstrap support via RunCompressibleBootstrap() for cluster installation
• Followed the same pattern as [release-4.17] OCPBUGS-38292: controller: default to runc when upgrading clusters from 4.17 to 4.18 #4715 (container runtime default change)

- How to verify it

• Install a 4.20 cluster and verify 50-master-compressible-kubelet-override and 50-worker-compressible-kubelet-override MachineConfigs are created
• Verify the MachineConfigs contain the current templated kubelet configuration with resolved template variables (e.g., ClusterDNSIP)
• Create a custom KubeletConfig and verify it overrides the compressible MachineConfig
• Upgrade from 4.20 to 4.21 and verify system reserved compressible resources are NOT enabled by default (due to the override MachineConfig)
• Delete the compressible MachineConfig after 4.21 upgrade and verify system reserved compressible becomes enabled with 4.21 defaults

- Description for the changelog

This patch enables 4.20 clusters to upgrade to 4.21 by creating a compressible kubelet MachineConfig that preserves 4.20 kubelet defaults. When upgrading to
4.21 (where system reserved compressible resources are enabled by default), this MachineConfig prevents automatic enablement. Customers can delete the
MachineConfig post-upgrade to adopt 4.21 defaults. This patch is mandatory for 4.20→4.21 upgrades; Cincinnati will block upgrades without it.

---

Testing Results

Fresh Installation:

• Created a release image from this branch and installed a new cluster
• Verified that compressible MachineConfigs (50-master-compressible-kubelet-override and 50-worker-compressible-kubelet-override) were successfully created

Upgrade Scenario:

• Created a release image from this branch and upgraded a cluster from 4.20 to this patched version
• Verified that compressible MachineConfigs were successfully created post-upgrade

Performance Profile Integration:

• Applied a Performance Profile and verified that reserved CPUs were correctly set in the kubeletconfig of worker nodes
• This confirms that the Node Tuning Operator (NTO) processing of Performance Profiles is not impacted by this change

All scenarios confirmed that the compressible MachineConfig creation works as expected without interfering with existing operators.

[openshift-ci]

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[openshift-ci]

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[ngopalak-redhat]

/test all

[ngopalak-redhat]

/test all

[openshift-ci]

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

Test name	Commit	Details	Required	Rerun command
ci/prow/e2e-gcp-op-1of2	b6094ff	link	true	/test e2e-gcp-op-1of2
ci/prow/e2e-aws-ovn-upgrade	b6094ff	link	true	/test e2e-aws-ovn-upgrade
ci/prow/e2e-gcp-op-2of2	b6094ff	link	true	/test e2e-gcp-op-2of2
ci/prow/e2e-gcp-op-single-node	b6094ff	link	true	/test e2e-gcp-op-single-node
ci/prow/periodics-images	b6094ff	link	true	/test periodics-images
ci/prow/bootstrap-unit	b6094ff	link	false	/test bootstrap-unit
ci/prow/images	b6094ff	link	true	/test images
ci/prow/okd-scos-images	b6094ff	link	true	/test okd-scos-images
ci/prow/e2e-aws-ovn	b6094ff	link	true	/test e2e-aws-ovn
ci/prow/e2e-hypershift	b6094ff	link	true	/test e2e-hypershift

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