1. Proposed title of this feature request

---> Changing cluster network IP address (CIDR) block on OVN-Kubernetes network cluster

2. What is the nature and description of the request?

---> Currently, the only documented and supported method to change cluster network IP address block is during offline SDN to OVN migration, using below command:

Update cluster CIDR block and network type of OVN-k8s

oc patch Network.config.openshift.io cluster --type='merge' --patch '{"spec": {"clusterNetwork": [ { "cidr": "10.56.0.0/15","hostPrefix": 24 } ], "networkType": "OVNKubernetes"}}' 

Refer to:

19.5.3.6. Migrating to the OVN-Kubernetes network plugin by using the offline migration method

https://docs.redhat.com/en/documentation/openshift_container_platform/4.16/html/networking/ovn-kubernetes-network-plugin#nw-ovn-kubernetes-migration_migrate-from-openshift-sdn

step 10.

Once the cluster is running with OVN-Kubernetes network, either migrated from SDN or built as OVN, there is no supported and official way to change change cluster network IP address block. The request is to allow changing cluster network IP address (CIDR) block on OVN-Kubernetes network cluster. At best using online method, which would be similar to mcp rollout, or OCP upgrade or OVN Limited Live Migration, where cluster nodes are rebooting in sequential order and no complete cluster downtime (power off of all nodes at once) is required.

3. Why does the customer need this? (List the business requirements here)

---> In our estate we have 638 clusters, with SDN networks, where cluster network IP address block has to be changed from "10.254.0.0/16" to "10.56.0.0/15".

These clusters are meant for OVN-Kubernetes migration too. Currently, we could use SDN to OVN offline migration method to achieve this goal. However, the SDN to OVN migration will be commenced using Limited Live Migration method, to avoid complete cluster downtime and minimise business impact.

As such, once mentioned clusters are migrated to OVN-Kubernetes network, there will still be a need to change cluster network IP address. Currently, once clusters are on OVN, then this is not possible at all. Feature allowing to change cluster network IP address on OVN-Kubernetes cluster, using online method at best.

4. List any affected packages or components.

---> Cluster internal networks, SDN, OVN