Migrating to the OpenShift SDN network plugin

How the migration process works
Migrating to the OpenShift SDN network plugin
Additional resources

As a cluster administrator, you can migrate to the OpenShift SDN network plugin from the OVN-Kubernetes network plugin.

To learn more about OpenShift SDN, read About the OpenShift SDN network plugin.

How the migration process works

The following table summarizes the migration process by segmenting between the user-initiated steps in the process and the actions that the migration performs in response.

Table 1. Migrating to OpenShift SDN from OVN-Kubernetes
User-initiated steps	Migration activity
Set the `migration` field of the `Network.operator.openshift.io` custom resource (CR) named `cluster` to `OpenShiftSDN`. Make sure the `migration` field is `null` before setting it to a value.	Cluster Network Operator (CNO) Updates the status of the `Network.config.openshift.io` CR named `cluster` accordingly. Machine Config Operator (MCO) Rolls out an update to the systemd configuration necessary for OpenShift SDN; the MCO updates a single machine per pool at a time by default, causing the total time the migration takes to increase with the size of the cluster.
Update the `networkType` field of the `Network.config.openshift.io` CR.	CNO Performs the following actions: Destroys the OVN-Kubernetes control plane pods. Deploys the OpenShift SDN control plane pods. Updates the Multus objects to reflect the new network plugin.
Reboot each node in the cluster.	Cluster As nodes reboot, the cluster assigns IP addresses to pods on the OpenShift SDN cluster network.

Cluster administrators can roll back to the OpenShift SDN Container Network Interface (CNI) network plugin by using the offline migration method. During the migration you must manually reboot every node in your cluster. With the offline migration method, there is some downtime, during which your cluster is unreachable.

Prerequisites

Install the OpenShift CLI (oc).
Access to the cluster as a user with the cluster-admin role.
A cluster installed on infrastructure configured with the OVN-Kubernetes network plugin.
A recent backup of the etcd database is available.
A reboot can be triggered manually for each node.
The cluster is in a known good state, without any errors.

Procedure

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

To prepare for the migration, set the migration field to null by entering the following command in your CLI:

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

Check that the migration status is empty for the Network.config.openshift.io object by entering the following command in your CLI. Empty command output indicates that the object is not in a migration operation.
```
$ oc get Network.config cluster -o jsonpath='{.status.migration}'
```

Apply the patch to the Network.operator.openshift.io object to set the network plugin back to OpenShift SDN by entering the following command in your CLI:

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

If you applied the patch to the Network.config.openshift.io object before the patch operation finalizes on the Network.operator.openshift.io object, the Cluster Network Operator (CNO) enters into a degradation state and this causes a slight delay until the CNO recovers from the degraded state.

Confirm that the migration status of the network plugin for the Network.config.openshift.io cluster object is OpenShiftSDN by entering the following command in your CLI:
```
$ oc get Network.config cluster -o jsonpath='{.status.migration.networkType}'
```
Apply the patch to the Network.config.openshift.io object to set the network plugin back to OpenShift SDN by entering the following command in your CLI:
```
$ oc patch Network.config.openshift.io cluster --type='merge' \
  --patch '{ "spec": { "networkType": "OpenShiftSDN" } }'
```
Optional: Disable automatic migration of several OVN-Kubernetes capabilities to the OpenShift SDN equivalents:
- Egress IPs
- Egress firewall
- Multicast
To disable automatic migration of the configuration for any of the previously noted OpenShift SDN features, specify the following keys:
```
$ oc patch Network.operator.openshift.io cluster --type='merge' \
  --patch '{
    "spec": {
      "migration": {
        "networkType": "OpenShiftSDN",
        "features": {
          "egressIP": <bool>,
          "egressFirewall": <bool>,
          "multicast": <bool>
        }
      }
    }
  }'
```
where:

bool: Specifies whether to enable migration of the feature. The default is true.
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 in your CLI. 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.

port

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":{
      "defaultNetwork":{
        "openshiftSDNConfig":{
          "mtu":1200
    }}}}'
```

Reboot each node in your cluster. You can reboot the nodes in your cluster with either of the following approaches:

With the oc rsh command, you can use a bash script similar to the following:

#!/bin/bash
readarray -t POD_NODES <<< "$(oc get pod -n openshift-machine-config-operator -o wide| grep daemon|awk '{print $1" "$7}')"

for i in "${POD_NODES[@]}"
do
  read -r POD NODE <<< "$i"
  until oc rsh -n openshift-machine-config-operator "$POD" chroot /rootfs shutdown -r +1
    do
      echo "cannot reboot node $NODE, retry" && sleep 3
    done
done

With the ssh command, you can use a bash script similar to the following. The script assumes that you have configured sudo to not prompt for a password.

#!/bin/bash

for ip in $(oc get nodes  -o jsonpath='{.items[*].status.addresses[?(@.type=="InternalIP")].address}')
do
   echo "reboot node $ip"
   ssh -o StrictHostKeyChecking=no core@$ip sudo shutdown -r -t 3
done

Wait until the Multus daemon set rollout completes. Run the following command to see your rollout status:

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

The name of the Multus pods is in the 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

After the nodes in your cluster have rebooted and the multus pods are rolled out, start all of the machine configuration pools by running the following commands::
- 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 in your CLI:
  $ 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.
  
  The value of the machineconfiguration.openshift.io/currentConfig field is equal to the value of the machineconfiguration.openshift.io/desiredConfig field.
2. To confirm that the machine config is correct, enter the following command in your CLI:
  $ oc get machineconfig <config_name> -o yaml
  where <config_name> is the name of the machine config from the machineconfiguration.openshift.io/currentConfig field.

Confirm that the migration succeeded:

To confirm that the network plugin is OpenShift SDN, enter the following command in your CLI. The value of status.networkType must be OpenShiftSDN.
```
$ oc get Network.config/cluster -o jsonpath='{.status.networkType}{"\n"}'
```
To confirm that the cluster nodes are in the Ready state, enter the following command in your CLI:
```
$ oc get nodes
```

If a node is stuck in the NotReady state, investigate the machine config daemon pod logs and resolve any errors.

To list the pods, enter the following command in your CLI:

$ oc get pod -n openshift-machine-config-operator

Example output

NAME                                         READY   STATUS    RESTARTS   AGE
machine-config-controller-75f756f89d-sjp8b   1/1     Running   0          37m
machine-config-daemon-5cf4b                  2/2     Running   0          43h
machine-config-daemon-7wzcd                  2/2     Running   0          43h
machine-config-daemon-fc946                  2/2     Running   0          43h
machine-config-daemon-g2v28                  2/2     Running   0          43h
machine-config-daemon-gcl4f                  2/2     Running   0          43h
machine-config-daemon-l5tnv                  2/2     Running   0          43h
machine-config-operator-79d9c55d5-hth92      1/1     Running   0          37m
machine-config-server-bsc8h                  1/1     Running   0          43h
machine-config-server-hklrm                  1/1     Running   0          43h
machine-config-server-k9rtx                  1/1     Running   0          43h

The names for the config daemon pods are in the following format: machine-config-daemon-<seq>. The <seq> value is a random five character alphanumeric sequence.

To display the pod log for each machine config daemon pod shown in the previous output, enter the following command in your CLI:
```
$ oc logs <pod> -n openshift-machine-config-operator
```
where pod is the name of a machine config daemon pod.
Resolve any errors in the logs shown by the output from the previous command.

To confirm that your pods are not in an error state, enter the following command in your CLI:
```
$ oc get pods --all-namespaces -o wide --sort-by='{.spec.nodeName}'
```
If pods on a node are in an error state, reboot that node.

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 in your CLI:
  $ oc patch Network.operator.openshift.io cluster --type='merge' \ --patch '{ "spec": { "migration": null } }'
2. To remove the OVN-Kubernetes configuration, enter the following command in your CLI:
  $ oc patch Network.operator.openshift.io cluster --type='merge' \ --patch '{ "spec": { "defaultNetwork": { "ovnKubernetesConfig":null } } }'
3. To remove the OVN-Kubernetes network provider namespace, enter the following command in your CLI:
  $ oc delete namespace openshift-ovn-kubernetes

Migrating to the OpenShift SDN network plugin

How the migration process works

Migrating to the OpenShift SDN network plugin

Additional resources