Hot plugging secondary network interfaces

You can add or remove secondary network interfaces without stopping your virtual machine (VM). OKD Virtualization supports hot plugging and hot unplugging for Linux bridge interfaces that use the VirtIO device driver.

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.

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

Hot plugging a bridge network interface using the CLI

Hot plug a bridge 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.

Procedure

1. 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>

2. Use the following command to hot plug a new network interface to the running VM. The virtctl addinterface command adds the new network interface to the VM and virtual machine instance (VMI) specification but does not attach it to the running VM.

   $ virtctl addinterface <vm_name> --network-attachment-definition-name <net_attach_def_name> --name <interface_name>

   where:

   <vm_name>

   Specifies the name of the VirtualMachine object.

   <net_attach_def_name>

   Specifies the name of NetworkAttachmentDefinition object.

   <interface_name>

   Specifies the name of the new network interface.

3. To attach the network interface to the running VM, live migrate the VM by using the following command:

   $ virtctl migrate <vm_name>

Verification

1. 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

2. Verify that the new interface is added to the VM by checking the VMI status:

   $ 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 bridge network interface using the CLI

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

Prerequisites

• Your VM must be running.

• The VM must be created on a cluster running OKD Virtualization 4.14 or later.

• The VM must have a bridge network interface attached.

Procedure

1. Hot unplug a bridge network interface by running the following command. The virtctl removeinterface command detaches the network interface from the guest, but the interface still exists in the pod.

   $ virtctl removeinterface <vm_name> --name <interface_name>

2. Remove the interface from the pod by migrating the VM:

   $ virtctl migrate <vm_name>

Additional resources

• Installing virtctl

• Creating a Linux bridge network attachment definition