oc-patch-add-nics-to-vms.md

I recently needed to use kubectl patch ... / oc patch ... to add an additional network interface to a Virtual Machine. Most of the patch examples I found on the internet resulted in the previous network interfaces being removed. This is the command and the accompanying patch-file that worked for me. The /- suffix on the path: component is the trick!

I took a lot of value from this blog post, Kubectl Patch: What You Can Use It for and How to Do It. Thanks Eric Goebelbecker!

N.B. make sure the NetworkAttachmentDefinition exists before doing this (oc get net-attach-def).

$ oc patch vm/name-of-my-vm --type=json --patch-file add-vm-nic.patch
virtualmachine.kubevirt.io/name-of-my-vm patched

$ cat add-vm-nic.patch
- op: add
  path: /spec/template/spec/networks/-
  value:
    name: my-network-name
    multus:
      networkName: my-network-name

- op: add
  path: /spec/template/spec/domain/devices/interfaces/-
  value:
    name: my-network-name
    model: virtio
    bridge: {}

This is what the patch looks like in YAML

spec:
  template:
    spec:
      networks:
        - name: my-network-name
          multus:
            networkName: my-network-name
      domain:
        devices:
          interfaces:
            - name: my-network-name
              model: virtio
              bridge: {}