Merge pull request #91562 from JoeAldinger/OSDOCS-10661-4.15

[enterprise-4.15] OSDOCS-10661-4.15:gateway mode added to migration procedure

Author: JoeAldinger

modules/checking-cluster-resources-before-initiating-limited-live-migration.adoc

@@ -133,4 +133,43 @@ $ oc get networkpolicy -n <namespace>
 ----
 NAME              POD-SELECTOR   AGE
 allow-multicast   app=my-app     11m
-----
+----
+
+. Optional: If your cluster uses static routes or routing policies in the host network, set `routingViaHost` spec to `true` and the `ipForwarding` spec to `Global` in the `gatewayConfig` object during migration.
++
+[source,terminal]
+----
+$ oc patch Network.operator.openshift.io cluster --type=merge \
+  --patch '{
+    "spec":{
+      "defaultNetwork":{
+        "ovnKubernetesConfig":{
+          "gatewayConfig": {
+            "ipForwarding": "Global",
+            "routingViaHost": true
+    }}}}}'
+----
+
+.. Verify that the `ipForwarding` spec has been set to `Global` and the `routingViaHost` spec to `true` by running the following command:
++
+[source,terminal]
+----
+$  oc get networks.operator.openshift.io cluster -o yaml | grep -A 5 "gatewayConfig"
+----
++
+.Example output
+[source,terminal]
+----
+apiVersion: operator.openshift.io/v1
+kind: Network
+metadata:
+  name: cluster
+# ...
+gatewayConfig:
+        ipForwarding: Global
+        ipv4: {}
+        ipv6: {}
+        routingViaHost: true
+      genevePort: 6081
+# ...
+----

modules/nw-ovn-kubernetes-live-migration-about.adoc

@@ -5,7 +5,7 @@
 [id="nw-ovn-kubernetes-live-migration-about_{context}"]
 = Limited live migration to the OVN-Kubernetes network plugin overview
 
-The limited live migration method is the process in which the OpenShift SDN network plugin and its network configurations, connections, and associated resources, are migrated to the OVN-Kubernetes network plugin without service interruption. For {product-title} 4.15, it is available for versions 4.15.31 and later. It is the preferred method for migrating from OpenShift SDN to OVN-Kubernetes. In the event that you cannot perform a limited live migration, you can use the offline migration method. 
+The limited live migration method is the process in which the OpenShift SDN network plugin and its network configurations, connections, and associated resources, are migrated to the OVN-Kubernetes network plugin without service interruption. For {product-title} 4.15, it is available for versions 4.15.31 and later. It is the preferred method for migrating from OpenShift SDN to OVN-Kubernetes. In the event that you cannot perform a limited live migration, you can use the offline migration method.
 
 [IMPORTANT]
 ====
@@ -98,4 +98,6 @@ During the limited live migration, both OVN-Kubernetes and OpenShift SDN run in
 
 * Like OpenShift SDN, OVN-Kubernetes resources such as `EgressFirewall` resources require `ClusterAdmin` privileges. Migrating from OpenShift SDN to OVN-Kubernetes does not automatically update role-base access control (RBAC) resources. OpenShift SDN resources granted to a project administrator through the `aggregate-to-admin` `ClusterRole` must be manually reviewed and adjusted, as these changes are not included in the migration process.
 +
-After migration, manual verification of RBAC resources is required. For information about setting the `aggregate-to-admin` ClusterRole after migration, see the example in link:https://access.redhat.com/solutions/6117301[How to allow project admins to manage Egressfirewall resources in RHOCP4].
+After migration, manual verification of RBAC resources is required. For information about setting the `aggregate-to-admin` ClusterRole after migration, see the example in link:https://access.redhat.com/solutions/6117301[How to allow project admins to manage Egressfirewall resources in RHOCP4].
+
+* When a cluster depends on static routes or routing policies in the host network so that pods can reach some destinations, users should set `routingViaHost` spec to `true` and `ipForwarding` to `Global` in the `gatewayConfig` object during migration. This will offload routing decision to host kernel. For more information, see link:https://access.redhat.com/solutions/7070870[Recommended practice to follow before Openshift SDN network plugin migration to OVNKubernetes plugin] (Red Hat Knowledgebase) and, see step five in "Checking cluster resources before initiating the limited live migration".