OSDOCS: Note that changing cgroupMode reboots nodes

[gauravsoniiii]

Changing nodes.config spec.cgroupMode updates MachineConfig kernel arguments; the MCO drains and reboots nodes. The procedure only described SchedulingDisabled → Ready, which omitted the reboot.

Jira:

• OSDOCS-21295

Description:

• Document that changing spec.cgroupMode on nodes.config/cluster causes the Machine Config Operator (MCO) to drain and reboot nodes.
• Previously, the "Configuring Linux cgroup" procedure only showed nodes entering Ready,SchedulingDisabled and returning to Ready, which can be read as a non-disruptive config apply. In practice, this change updates MachineConfig kernelArguments, so nodes must reboot for the new cgroup configuration to take effect.

Version(s):

• 4.14, 4.15, 4.16, 4.17, 4.18

Issue:

• The procedure "Configuring Linux cgroup" (nodes-clusters-cgroups-2) does not state that changing spec.cgroupMode on nodes.config/cluster causes the Machine Config Operator to drain and reboot nodes.

• Changing cgroupMode renders new MachineConfigs with updated kernelArguments (systemd.unified_cgroup_hierarchy, cgroup_no_v1, etc.). Kernel-argument changes only take effect after a full node reboot (standard MCO cordon → drain → reboot → uncordon behavior). The published Verification steps only mention Ready,SchedulingDisabled and return to Ready, which customers read as a non-disruptive config apply.

Link to docs preview:

QE review:

• QE has approved this change.

Additional information:

• Doc URL: https://docs.redhat.com/en/documentation/openshift_container_platform/4.18/html/nodes/working-with-clusters#nodes-clusters-cgroups-2_nodes-cluster-cgroups-2
• File: modules/nodes-clusters-cgroups-2.adoc
• Please cherry-pick to: enterprise-4.14, enterprise-4.15, enterprise-4.16, enterprise-4.17, enterprise-4.18

[openshift-ci]

Hi @gauravsoniiii. Thanks for your PR.

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[openshift-ci]

@gauravsoniiii: The label(s) `/label peer-review-needed

cannot be applied. These labels are supported:acknowledge-critical-fixes-only, platform/aws, platform/azure, platform/baremetal, platform/google, platform/libvirt, platform/openstack, ga, tide/merge-method-merge, tide/merge-method-rebase, tide/merge-method-squash, px-approved, docs-approved, qe-approved, ux-approved, no-qe, rebase/manual, cluster-config-api-changed, run-integration-tests, verified, ready-for-human-review, approved, backport-risk-assessed, bugzilla/valid-bug, cherry-pick-approved, cloud-experts, cnv, dev-tools, distributed-tracing, ims, jira/skip-dependent-bug-check, jira/valid-bug, merge-review-in-progress, merge-review-needed, mtc, multi-arch, oadp, ok-to-test, rhacs, rhv, sd-docs, serverless, service-mesh, sme-review-done, sme-review-needed, stability-fix-approved, staff-eng-approved, telco. Is this label configured under labels -> additional_labelsorlabels -> restricted_labelsinplugin.yaml`?

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[gauravsoniiii]

/label merge-review-needed

[openshift-ci]

@gauravsoniiii: The label(s) merge-review-needed cannot be applied or removed, because you are not in one of the allowed teams and are not an allowed user. Must be a member of one of these teams: team-red-hat

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In response to this:

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