support for Knative VMs

[raffaelespazzoli]

What would you like to be added:

I'd like external-dns to manage dns entries for Knative VMs. Knative VMs are tipycally managed as pets and as such that receive individual FQDNs.

A Knative VM is a pod and when it is attached to the main pod network, the current support that we have from the Kube DNS is fine.

But more often that not VMs are attached to Multus secondary networks typically via bridge.

In this situation the VM will either have a statically assigned IP or receive an IP from DHCP and it would be great to be able to automate the assignment of FQDN to that IP. In fact the VM could be attached to multiple network and every virtual interface can have an IP and may need an FQDN.

VirtualMachineInstances is the CR that store the status of the interfaces as this:

  interfaces:
    - infoSource: 'domain, guest-agent, multus-status'
      interfaceName: eth0
      ipAddress: 10.100.200.3
      ipAddresses:
        - 10.100.200.3
      mac: '02:a5:cf:00:00:02'
      name: nic-harlequin-woodpecker-12
      queueCount: 1

It would be great if by annotating the VM we could get the IP captured in the VMI status to be assigned a name.

Why is this needed:

With the increase of organization interested in running VMs on Kubernetes naming a VM is becoming a common use case that does not have a Kubernetes native solution yet.