Migrating from the OpenShift SDN network plugin

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

To learn more about OVN-Kubernetes, read About the OVN-Kubernetes network plugin.

Migration to the OVN-Kubernetes network plugin

Migrating to the OVN-Kubernetes network plugin is a manual process that includes some downtime during which your cluster is unreachable. Although a rollback procedure is provided, the migration is intended to be a one-way process.

A migration to the OVN-Kubernetes network plugin is supported on the following platforms:

• Bare metal hardware

• Amazon Web Services (AWS)

• Google Cloud Platform (GCP)

• IBM Cloud®

• Microsoft Azure

• OpenStack

• VMware vSphere

Considerations for migrating to the OVN-Kubernetes network plugin

If you have more than 150 nodes in your OKD cluster, then open a support case for consultation on your migration to the OVN-Kubernetes network plugin.

The subnets assigned to nodes and the IP addresses assigned to individual pods are not preserved during the migration.

While the OVN-Kubernetes network plugin implements many of the capabilities present in the OpenShift SDN network plugin, the configuration is not the same.

• If your cluster uses any of the following OpenShift SDN network plugin capabilities, you must manually configure the same capability in the OVN-Kubernetes network plugin:

  • Namespace isolation

  • Egress router pods

• If your cluster or surrounding network uses any part of the 100.64.0.0/16 address range, you must choose another unused IP range by specifying the v4InternalSubnet spec under the spec.defaultNetwork.ovnKubernetesConfig object definition. OVN-Kubernetes uses the IP range 100.64.0.0/16 internally by default.

The following sections highlight the differences in configuration between the aforementioned capabilities in OVN-Kubernetes and OpenShift SDN network plugins.

Namespace isolation

OVN-Kubernetes supports only the network policy isolation mode.

Egress IP addresses

OpenShift SDN supports two different Egress IP modes:

• In the automatically assigned approach, an egress IP address range is assigned to a node.

• In the manually assigned approach, a list of one or more egress IP addresses is assigned to a node.

The migration process supports migrating Egress IP configurations that use the automatically assigned mode.

The differences in configuring an egress IP address between OVN-Kubernetes and OpenShift SDN is described in the following table:

For more information on using egress IP addresses in OVN-Kubernetes, see “Configuring an egress IP address”.

Egress network policies

The difference in configuring an egress network policy, also known as an egress firewall, between OVN-Kubernetes and OpenShift SDN is described in the following table:

Egress router pods

OVN-Kubernetes supports egress router pods in redirect mode. OVN-Kubernetes does not support egress router pods in HTTP proxy mode or DNS proxy mode.

When you deploy an egress router with the Cluster Network Operator, you cannot specify a node selector to control which node is used to host the egress router pod.

Multicast

The difference between enabling multicast traffic on OVN-Kubernetes and OpenShift SDN is described in the following table:

For more information on using multicast in OVN-Kubernetes, see “Enabling multicast for a project”.

Network policies

OVN-Kubernetes fully supports the Kubernetes NetworkPolicy API in the networking.k8s.io/v1 API group. No changes are necessary in your network policies when migrating from OpenShift SDN.

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.

If a rollback to OpenShift SDN is required, the following table describes the process.

Migrating to the OVN-Kubernetes network plugin

As a cluster administrator, you can change the network plugin for your cluster to OVN-Kubernetes. During the migration, you must reboot every node in your cluster.

Prerequisites

• A cluster configured with the OpenShift SDN CNI network plugin in the network policy isolation mode.

• Install the OpenShift CLI (oc).

• Access to the cluster as a user with the cluster-admin role.

• 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.

• On all cloud platforms after updating software, a security group rule must be in place to allow UDP packets on port 6081 for all nodes.

Procedure

1. To backup the configuration for the cluster network, enter the following command:

   $ oc get Network.config.openshift.io cluster -o yaml > cluster-openshift-sdn.yaml

2. To prepare all the nodes for the migration, set the migration field on the Cluster Network Operator configuration object by entering the following command:

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

   This step does not deploy OVN-Kubernetes immediately. Instead, specifying the migration field triggers the Machine Config Operator (MCO) to apply new machine configs to all the nodes in the cluster in preparation for the OVN-Kubernetes deployment.

3. Optional: You can disable automatic migration of several OpenShift SDN capabilities to the OVN-Kubernetes 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": "OVNKubernetes",
           "features": {
             "egressIP": <bool>,
             "egressFirewall": <bool>,
             "multicast": <bool>
           }
         }
       }
     }'

   where:

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

4. Optional: You can customize the following settings for OVN-Kubernetes to meet your network infrastructure requirements:

   • Maximum transmission unit (MTU). Consider the following before customizing the MTU for this optional step:

     • If you use the default MTU, and you want to keep the default MTU during migration, this step can be ignored.

     • If you used a custom MTU, and you want to keep the custom MTU during migration, you must declare the custom MTU value in this step.

     • This step does not work if you want to change the MTU value during migration. Instead, you must first follow the instructions for “Changing the cluster MTU”. You can then keep the custom MTU value by performing this procedure and declaring the custom MTU value in this step.

       OpenShift-SDN and OVN-Kubernetes have different overlay overhead. MTU values should be selected by following the guidelines found on the “MTU value selection” page.

   • Geneve (Generic Network Virtualization Encapsulation) overlay network port

   • OVN-Kubernetes IPv4 internal subnet

   • OVN-Kubernetes IPv6 internal subnet

   To customize either of the previously noted settings, enter and customize 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":{
           "ovnKubernetesConfig":{
             "mtu":<mtu>,
             "genevePort":<port>,
             "v4InternalSubnet":"<ipv4_subnet>",
             "v6InternalSubnet":"<ipv6_subnet>"
       }}}}'

   where:

   mtu

   The MTU for the Geneve 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 100 less than the smallest node MTU value.

   port

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

   ipv4_subnet

   An IPv4 address range for internal use by OVN-Kubernetes. You must ensure that the IP address range does not overlap with any other subnet used by your OKD installation. The IP address range must be larger than the maximum number of nodes that can be added to the cluster. The default value is 100.64.0.0/16.

   ipv6_subnet

   An IPv6 address range for internal use by OVN-Kubernetes. You must ensure that the IP address range does not overlap with any other subnet used by your OKD installation. The IP address range must be larger than the maximum number of nodes that can be added to the cluster. The default value is fd98::/48.

   Example patch command to update mtu field

   $ oc patch Network.operator.openshift.io cluster --type=merge \
     --patch '{
       "spec":{
         "defaultNetwork":{
           "ovnKubernetesConfig":{
             "mtu":1200
       }}}}'

5. As the MCO updates machines in each machine config pool, it reboots each node one by one. You must wait until all the nodes are updated. Check the machine config pool status by entering the following command:

   $ oc get mcp

   A successfully updated node has the following status: UPDATED=true, UPDATING=false, DEGRADED=false.

   By default, the MCO updates one machine per pool at a time, causing the total time the migration takes to increase with the size of the cluster.

6. 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.

      • 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:

      $ oc get machineconfig <config_name> -o yaml | grep ExecStart

      where <config_name> is the name of the machine config from the machineconfiguration.openshift.io/currentConfig field.

      The machine config must include the following update to the systemd configuration:

      ExecStart=/usr/local/bin/configure-ovs.sh OVNKubernetes

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

      1. To list the pods, enter the following command:

         $ 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.

      2. Display the pod log for the first machine config daemon pod shown in the previous output by enter the following command:

         $ oc logs <pod> -n openshift-machine-config-operator

         where pod is the name of a machine config daemon pod.

      3. Resolve any errors in the logs shown by the output from the previous command.

1. To start the migration, configure the OVN-Kubernetes network plugin by using one of the following commands:

   • To specify the network provider without changing the cluster network IP address block, enter the following command:

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

   • To specify a different cluster network IP address block, enter the following command:

     $ oc patch Network.config.openshift.io cluster \
       --type='merge' --patch '{
         "spec": {
           "clusterNetwork": [
             {
               "cidr": "<cidr>",
               "hostPrefix": <prefix>
             }
           ],
           "networkType": "OVNKubernetes"
         }
       }'

     where cidr is a CIDR block and prefix is the slice of the CIDR block apportioned to each node in your cluster. You cannot use any CIDR block that overlaps with the 100.64.0.0/16 CIDR block because the OVN-Kubernetes network provider uses this block internally.

     You cannot change the service network address block during the migration.

2. Verify that the Multus daemon set rollout is complete before continuing with subsequent steps:

   $ 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

3. To complete changing the network plugin, 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

4. Confirm that the migration succeeded:

   1. To confirm that the network plugin is OVN-Kubernetes, enter the following command. The value of status.networkType must be OVNKubernetes.

      $ oc get network.config/cluster -o jsonpath='{.status.networkType}{"\n"}'

   2. To confirm that the cluster nodes are in the Ready state, enter the following command:

      $ oc get nodes

   3. To confirm that your pods are not in an error state, enter the following command:

      $ oc get pods --all-namespaces -o wide --sort-by='{.spec.nodeName}'

      If pods on a node are in an error state, reboot that node.

   4. To confirm that all of the cluster Operators are not in an abnormal state, enter the following command:

      $ oc get co

      The status of every cluster Operator must be the following: AVAILABLE="True", PROGRESSING="False", DEGRADED="False". If a cluster Operator is not available or degraded, check the logs for the cluster Operator for more information.

5. 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 CNO configuration object, enter the following command:

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

   2. To remove custom configuration for the OpenShift SDN network provider, enter the following command:

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

   3. To remove the OpenShift SDN network provider namespace, enter the following command:

      $ oc delete namespace openshift-sdn

Additional resources

• Configuration parameters for the OVN-Kubernetes network plugin

• Backing up etcd

• About network policy

• Changing the cluster MTU

• MTU value selection

• OVN-Kubernetes capabilities

  • Configuring an egress IP address

  • Configuring an egress firewall for a project

  • Enabling multicast for a project

• OpenShift SDN capabilities

  • Configuring egress IPs for a project

  • Configuring an egress firewall for a project

  • Enabling multicast for a project

• [Network [operator.openshift.io/v1]($fd23142133a578a6.md#network-operator-openshift-io-v1)]