Rolling back to the OpenShift SDN network provider

As a cluster administrator, you can rollback your cluster to the OpenShift SDN Container Network Interface (CNI) cluster network provider. During the rollback, you must reboot every node in your cluster.

Prerequisites

Install the OpenShift CLI ().
Access to the cluster as a user with the cluster-admin role.
A cluster installed on infrastructure configured with the OVN-Kubernetes CNI cluster network provider.

Procedure

Stop all of the machine configuration pools managed by the Machine Config Operator (MCO):
- Stop the master configuration pool:
- Stop the worker machine configuration pool:
```
$ oc patch MachineConfigPool worker --type='merge' --patch \
  '{ "spec":{ "paused" :true } }'
```

To start the migration, set the cluster network provider back to OpenShift SDN by entering the following commands:

$ oc patch Network.operator.openshift.io cluster --type='merge' \
  --patch '{ "spec": { "migration": { "networkType": "OpenShiftSDN" } } }'
$ oc patch Network.config.openshift.io cluster --type='merge' \
  --patch '{ "spec": { "networkType": "OpenShiftSDN" } }'

Optional: You can customize the following settings for OpenShift SDN to meet your network infrastructure requirements:
- Maximum transmission unit (MTU)
- VXLAN port
To customize either or both of the previously noted settings, customize and enter the following command. If you do not need to change the default value, omit the key from the patch.
```
$ oc patch Network.operator.openshift.io cluster --type=merge \
  --patch '{
    "spec":{
      "defaultNetwork":{
        "openshiftSDNConfig":{
          "mtu":<mtu>,
          "vxlanPort":<port>
    }}}}'
```
mtu

The MTU for the VXLAN overlay network. This value is normally configured automatically, but if the nodes in your cluster do not all use the same MTU, then you must set this explicitly to 50 less than the smallest node MTU value.

The UDP port for the VXLAN overlay network. If a value is not specified, the default is 4789. The port cannot be the same as the Geneve port that is used by OVN-Kubernetes. The default value for the Geneve port is 6081.

Example patch command
```
$ oc patch Network.operator.openshift.io cluster --type=merge \
  --patch '{
    "spec":{
        "openshiftSDNConfig":{
    }}}}'
```

Wait until the Multus daemon set rollout completes.

$ oc -n openshift-multus rollout status daemonset/multus

The name of the Multus pods is in form of multus-<xxxxx> where <xxxxx> is a random sequence of letters. It might take several moments for the pods to restart.

Example output

Waiting for daemon set "multus" rollout to finish: 1 out of 6 new pods have been updated...
...
Waiting for daemon set "multus" rollout to finish: 5 of 6 updated pods are available...
daemon set "multus" successfully rolled out

To complete the rollback, reboot each node in your cluster. For example, you could use a bash script similar to the following. The script assumes that you can connect to each host by using ssh and that you have configured sudo to not prompt for a password.

If ssh access is not available, you might be able to reboot each node through the management portal for your infrastructure provider.
After the nodes in your cluster have rebooted, start all of the machine configuration pools:
- Start the master configuration pool:
```
$ oc patch MachineConfigPool master --type='merge' --patch \
  '{ "spec": { "paused": false } }'
```
- Start the worker configuration pool:
```
$ oc patch MachineConfigPool worker --type='merge' --patch \
  '{ "spec": { "paused": false } }'
```
As the MCO updates machines in each config pool, it reboots each node.

By default the MCO updates a single machine per pool at a time, so the time that the migration requires to complete grows with the size of the cluster.
Confirm the status of the new machine configuration on the hosts:
1. To list the machine configuration state and the name of the applied machine configuration, enter the following command:
```
$ oc describe node | egrep "hostname|machineconfig"
```
  Example output
```
kubernetes.io/hostname=master-0
machineconfiguration.openshift.io/currentConfig: rendered-master-c53e221d9d24e1c8bb6ee89dd3d8ad7b
machineconfiguration.openshift.io/desiredConfig: rendered-master-c53e221d9d24e1c8bb6ee89dd3d8ad7b
machineconfiguration.openshift.io/reason:
machineconfiguration.openshift.io/state: Done
```
  Verify that the following statements are true:
  - The value of machineconfiguration.openshift.io/state field is Done.
2. To confirm that the machine config is correct, enter the following command:
```
$ oc get machineconfig <config_name> -o yaml
```
  where <config_name> is the name of the machine config from the field.
Complete the following steps only if the migration succeeds and your cluster is in a good state:
1. To remove the migration configuration from the Cluster Network Operator configuration object, enter the following command:
```
$ oc patch Network.operator.openshift.io cluster --type='merge' \
  --patch '{ "spec": { "migration": null } }'
```
2. To remove the OVN-Kubernetes configuration, enter the following command:
```
$ oc patch Network.operator.openshift.io cluster --type='merge' \
```

Rolling back to the OpenShift SDN cluster network provider

Rolling back to the OpenShift SDN network provider