TELCODOCS#2230: Coordinating reboots for configuration changes

Author: sr1kar99

Diff for: edge_computing/policygenerator_for_ztp/ztp-configuring-managed-clusters-policygenerator.adoc

@@ -55,6 +55,8 @@ include::modules/ztp-customizing-a-managed-site-using-pgt.adoc[leveloffset=+1]
 
 include::modules/ztp-monitoring-policy-deployment-progress.adoc[leveloffset=+1]
 
+include::modules/ztp-coordinating-reboots-for-config-changes.adoc[leveloffset=+1]
+
 include::modules/ztp-validating-the-generation-of-configuration-policy-crs.adoc[leveloffset=+1]
 
 include::modules/ztp-restarting-policies-reconciliation.adoc[leveloffset=+1]

Diff for: modules/defer-applicaton-tuning-example.adoc

@@ -55,4 +55,8 @@ spec:
 
 <1> The `include` directive is used to inherit the `openshift-node-performance-performance` profile. This is a best practice to ensure that the profile is not missing any required settings.
 <2> The `kernel.shmmni` sysctl parameter is being changed to `8192`.
-<3> The `machineConfigLabels` field is used to target the `worker-cnf` role. Configure a `MachineConfigPool` resource to ensure the profile is applied only to the correct nodes.
+<3> The `machineConfigLabels` field is used to target the `worker-cnf` role. Configure a `MachineConfigPool` resource to ensure the profile is applied only to the correct nodes.
+
+You can use {cgu-operator-full} to coordinate reboots across a fleet of spoke clusters when configuration changes require a reboot. These configuration changes include updates to tuning profiles that modify kernel parameters or system behavior.{cgu-operator} ensures that only nodes with a degraded tuned profile, indicating a reboot is needed, are rebooted. Instead of rebooting nodes after each individual change, you can apply all configuration updates through policies and then trigger a single, coordinated reboot. 
+
+For more information about coordinated reboots, see xref:../../edge_computing/policygenerator_for_ztp/ztp-configuring-managed-clusters-policygenerator.adoc#ztp-coordinating-reboots-for-config-changes_ztp-configuring-managed-clusters-policygenerator[Coordinating reboots for configuration changes]

Diff for: modules/ztp-coordinating-reboots-for-config-changes.adoc

@@ -0,0 +1,40 @@
+// Module included in the following assemblies:
+//
+// * scalability_and_performance/ztp_far_edge/ztp-configuring-managed-clusters-policies.adoc
+
+:_mod-docs-content-type: PROCEDURE
+[id="ztp-coordinating-reboots-for-config-changes_{context}"]
+= Coordinating reboots for configuration changes
+
+You can use {cgu-operator-full} to coordinate reboots across a fleet of spoke clusters when configuration changes require a reboot.
+
+The following types of configuration changes typically require a reboot:
+
+* Updates to tuning profiles that modify kernel parameters or system behavior.
+* Kubelet configuration updates.
+* Node-level changes delivered through `MachineConfig`, such as `sysctl` settings or system service changes.
+
+{cgu-operator} ensures that only nodes with a degraded tuned profile, indicating a reboot is needed, are rebooted.
+
+Instead of rebooting nodes after each individual change, you can apply all configuration updates through policies and then trigger a single, coordinated reboot. 
+
+.Prerequisites
+
+* You have installed the {oc-first}.
+* You have logged in to the hub cluster as a user with `cluster-admin` privileges.
+* You have deployed and configured {cgu-operator}.
+
+.Procedure
+
+. Create the configuration policies and policy bindings for the tuning or configuration changes.
+
+. Create a reboot policy on the hub cluster. This policy checks for degraded tuned profiles that indicate a reboot is needed.
+
+. Create and apply the `ClusterGroupUpgrade` (CGU) custom resource (CR). In the `spec.managedPolicies` list, include all relevant configuration policies first, followed by the reboot policy and the optional `mcp-validator` policy.
++
+After you apply the CGU custom resource, {cgu-operator} rolls out the configuration policies in order. When all policies are compliant, {cgu-operator} applies the reboot policy. This triggers a reboot of all nodes in the specified `MachineConfigPool`.
+
+.Verification
+
+* Confirm that all nodes in the `MachineConfigPool` have rebooted.
+* Verify that the `MachineConfigPool` reaches the `Updated` state.