Hot plugging secondary network interfaces

VirtIO limitations
Hot plugging a secondary network interface by using the CLI
Hot unplugging a secondary network interface by using the CLI
Additional resources

You can add or remove secondary network interfaces without stopping your virtual machine (VM). OKD Virtualization supports hot plugging and hot unplugging for secondary interfaces that use bridge binding and the VirtIO device driver. OKD Virtualization also supports hot plugging secondary interfaces that use SR-IOV binding. To hot plug or hot unplug a secondary interface, you must have permission to create and list VirtualMachineInstanceMigration objects.

Hot unplugging is not supported for Single Root I/O Virtualization (SR-IOV) interfaces.

VirtIO limitations

Each VirtIO interface uses one of the limited Peripheral Connect Interface (PCI) slots in the VM. There are a total of 32 slots available. The PCI slots are also used by other devices and must be reserved in advance, therefore slots might not be available on demand. OKD Virtualization reserves up to four slots for hot plugging interfaces. This includes any existing plugged network interfaces. For example, if your VM has two existing plugged interfaces, you can hot plug two more network interfaces.

The actual number of slots available for hot plugging also depends on the machine type. For example, the default PCI topology for the q35 machine type supports hot plugging one additional PCIe device. For more information on PCI topology and hot plug support, see the libvirt documentation.

If you restart the VM after hot plugging an interface, that interface becomes part of the standard network interfaces.

Hot plugging a secondary network interface by using the CLI

Hot plug a secondary network interface to a virtual machine (VM) while the VM is running.

Prerequisites

A network attachment definition is configured in the same namespace as your VM.
You have installed the virtctl tool.
You have installed the OpenShift CLI (oc).

Procedure

If the VM to which you want to hot plug the network interface is not running, start it by using the following command:
```
$ virtctl start <vm_name> -n <namespace>
```

Use your preferred text editor to edit the VirtualMachine manifest, as shown in the following example:

Example VM configuration

apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
  name: vm-fedora
template:
  spec:
    domain:
      devices:
        interfaces:
        - name: defaultnetwork
          masquerade: {}
        # new interface
        - name: <secondary_nic> (1)
          bridge: {}
    networks:
    - name: defaultnetwork
      pod: {}
    # new network
    - name: <secondary_nic> (2)
      multus:
        networkName: <nad_name> (3)
# ...

1	Specifies the name of the new network interface.
2	Specifies the name of the network. This must be the same as the `name` of the new network interface that you defined in the `template.spec.domain.devices.interfaces` list.
3	Specifies the name of the `NetworkAttachmentDefinition` object.

Save your changes and exit the editor.
For the new configuration to take effect, apply the changes by running the following command. Applying the changes triggers automatic VM live migration and attaches the network interface to the running VM.
```
$ oc apply -f <filename>.yaml
```
where:

<filename>

Specifies the name of your VirtualMachine manifest YAML file.

Verification

Verify that the VM live migration is successful by using the following command:

$ oc get VirtualMachineInstanceMigration -w

Example output

NAME                        PHASE             VMI
kubevirt-migrate-vm-lj62q   Scheduling        vm-fedora
kubevirt-migrate-vm-lj62q   Scheduled         vm-fedora
kubevirt-migrate-vm-lj62q   PreparingTarget   vm-fedora
kubevirt-migrate-vm-lj62q   TargetReady       vm-fedora
kubevirt-migrate-vm-lj62q   Running           vm-fedora
kubevirt-migrate-vm-lj62q   Succeeded         vm-fedora

Verify that the new interface is added to the VM by checking the status of the virtual machine instance (VMI):

$ oc get vmi vm-fedora -ojsonpath="{ @.status.interfaces }"

Example output

[
  {
    "infoSource": "domain, guest-agent",
    "interfaceName": "eth0",
    "ipAddress": "10.130.0.195",
    "ipAddresses": [
      "10.130.0.195",
      "fd02:0:0:3::43c"
    ],
    "mac": "52:54:00:0e:ab:25",
    "name": "default",
    "queueCount": 1
  },
  {
    "infoSource": "domain, guest-agent, multus-status",
    "interfaceName": "eth1",
    "mac": "02:d8:b8:00:00:2a",
    "name": "bridge-interface", (1)
    "queueCount": 1
  }
]

1	The hot plugged interface appears in the VMI status.

Hot unplugging a secondary network interface by using the CLI

You can remove a secondary network interface from a running virtual machine (VM).