DNS for Services and VirtualMachineInstances

Creating unique DNS entries per VirtualMachineInstance

In order to create unique DNS entries per VirtualMachineInstance, it is possible to set spec.hostname and spec.subdomain. If a subdomain is set and a headless service with a name, matching the subdomain, exists, kube-dns will create unique DNS entries for every VirtualMachineInstance which matches the selector of the service. Have a look at the DNS for Services and Pods documentation for additional information.

The following example consists of a VirtualMachine and a headless Service which matches the labels and the subdomain of the VirtualMachineInstance:

apiVersion: kubevirt.io/v1alpha3
kind: VirtualMachineInstance
  name: vmi-fedora
    expose: me
  hostname: "myvmi"
  subdomain: "mysubdomain"
      - disk:
          bus: virtio
        name: containerdisk
      - disk:
          bus: virtio
        name: cloudinitdisk
        memory: 1024M
  terminationGracePeriodSeconds: 0
  - name: containerdisk
      image: kubevirt/fedora-cloud-registry-disk-demo:latest
  - cloudInitNoCloud:
      userDataBase64: IyEvYmluL2Jhc2gKZWNobyAiZmVkb3JhOmZlZG9yYSIgfCBjaHBhc3N3ZAo=
    name: cloudinitdisk
apiVersion: v1
kind: Service
  name: mysubdomain
    expose: me
  clusterIP: None
  - name: foo # Actually, no port is needed.
    port: 1234
    targetPort: 1234

As a consequence, when we enter the VirtualMachineInstance via e.g. virtctl console vmi-fedora and ping myvmi.mysubdomain we see that we find a DNS entry for myvmi.mysubdomain.default.svc.cluster.local which points to, which is the IP of the VirtualMachineInstance (not of the Service):

[fedora@myvmi ~]$ ping myvmi.mysubdomain
PING myvmi.mysubdomain.default.svc.cluster.local ( 56(84) bytes of data.
64 bytes from myvmi.mysubdomain.default.svc.cluster.local ( icmp_seq=1 ttl=64 time=0.029 ms
[fedora@myvmi ~]$ ip a
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 0a:58:0a:f4:00:39 brd ff:ff:ff:ff:ff:ff
    inet brd scope global dynamic eth0
       valid_lft 86313556sec preferred_lft 86313556sec
    inet6 fe80::858:aff:fef4:39/64 scope link
       valid_lft forever preferred_lft forever

So spec.hostname and spec.subdomain get translated to a DNS A-record of the form <vmi.spec.hostname>.<vmi.spec.subdomain>.<vmi.metadata.namespace>.svc.cluster.local. If no spec.hostname is set, then we fall back to the VirtualMachineInstance name itself. The resulting DNS A-record looks like this then: <vmi.metadata.name>.<vmi.spec.subdomain>.<vmi.metadata.namespace>.svc.cluster.local.