MIG-747: Cached clients (MTC 1.5.0)

migrating_from_ocp_3_to_4/advanced-migration-options-3-4.adoc

@@ -43,5 +43,6 @@ include::modules/migration-writing-ansible-playbook-hook.adoc[leveloffset=+2]
 include::modules/migration-changing-migration-plan-limits.adoc[leveloffset=+1]
 include::modules/migration-excluding-resources.adoc[leveloffset=+1]
 include::modules/migration-enabling-pv-resizing-dvm.adoc[leveloffset=+1]
+include::modules/migration-enabling-cached-kubernetes-clients.adoc[leveloffset=+1]
 
 :advanced-migration-options-3-4!:

migration-toolkit-for-containers/advanced-migration-options-mtc.adoc

@@ -42,3 +42,4 @@ include::modules/migration-writing-ansible-playbook-hook.adoc[leveloffset=+2]
 include::modules/migration-changing-migration-plan-limits.adoc[leveloffset=+1]
 include::modules/migration-excluding-resources.adoc[leveloffset=+1]
 include::modules/migration-enabling-pv-resizing-dvm.adoc[leveloffset=+1]
+include::modules/migration-enabling-cached-kubernetes-clients.adoc[leveloffset=+1]

modules/migration-enabling-cached-kubernetes-clients.adoc

@@ -0,0 +1,44 @@
+// Module included in the following assemblies:
+//
+// * migrating_from_ocp_3_to_4/advanced-migration-options-3-4.adoc
+// * migration-toolkit-for-containers/advanced-migration-options-mtc.adoc
+
+[id="migration-enabling-cached-kubernetes-clients_{context}"]
+= Enabling cached Kubernetes clients
+
+You can enable cached Kubernetes clients in the `MigrationController` custom resource (CR) for improved performance during migration. The greatest performance benefit is displayed when migrating between clusters in different regions or with significant network latency.
+
+[NOTE]
+====
+Delegated tasks, for example, Rsync backup for direct volume migration or Velero backup and restore, however, do not show improved performance with cached clients.
+====
+
+Cached clients require extra memory because the `MigrationController` CR caches all API resources that are required for interacting with `MigCluster` CRs. Requests that are normally sent to the API server are directed to the cache instead. The cache watches the API server for updates.
+
+You can increase the memory limits and requests of the `MigrationController` CR if `OOMKilled` errors occur after you enable cached clients.
+
+.Procedure
+
+. Enable cached clients by running the following command:
++
+[source,terminal]
+----
+$ oc -n openshift-migration patch migrationcontroller migration-controller --type=json --patch \
+  '[{ "op": "replace", "path": "/spec/mig_controller_enable_cache", "value": true}]'
+----
+
+. Optional: Increase the `MigrationController` CR memory limits by running the following command:
++
+[source,terminal]
+----
+$ oc -n openshift-migration patch migrationcontroller migration-controller --type=json --patch \
+  '[{ "op": "replace", "path": "/spec/mig_controller_limits_memory", "value": <10Gi>}]'
+----
+
+. Optional: Increase the `MigrationController` CR memory requests by running the following command:
++
+[source,terminal]
+----
+$ oc -n openshift-migration patch migrationcontroller migration-controller --type=json --patch \
+  '[{ "op": "replace", "path": "/spec/mig_controller_requests_memory", "value": <350Mi>}]'
+----