DNS records

In order to create unique DNS records 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:

  1. apiVersion: kubevirt.io/v1
  2. kind: VirtualMachineInstance
  3. metadata:
  4.   name: vmi-fedora
  5.   labels:
  6.     expose: me
  7. spec:
  8.   hostname: "myvmi"
  9.   subdomain: "mysubdomain"
  10.   domain:
  11.     devices:
  12.       disks:
  13.       - disk:
  14.           bus: virtio
  15.         name: containerdisk
  16.       - disk:
  17.           bus: virtio
  18.         name: cloudinitdisk
  19.     resources:
  20.       requests:
  21.         memory: 1024M
  22.   terminationGracePeriodSeconds: 0
  23.   volumes:
  24.   - name: containerdisk
  25.     containerDisk:
  26.       image: kubevirt/fedora-cloud-registry-disk-demo:latest
  27.   - cloudInitNoCloud:
  28.       userDataBase64: IyEvYmluL2Jhc2gKZWNobyAiZmVkb3JhOmZlZG9yYSIgfCBjaHBhc3N3ZAo=
  29.     name: cloudinitdisk
  30. ---
  31. apiVersion: v1
  32. kind: Service
  33. metadata:
  34.   name: mysubdomain
  35. spec:
  36.   selector:
  37.     expose: me
  38.   clusterIP: None
  39.   ports:
  40.   - name: foo # Actually, no port is needed.
  41.     port: 1234
  42.     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 10.244.0.57, which is the IP of the VirtualMachineInstance (not of the Service):

  1. [fedora@myvmi ~]$ ping myvmi.mysubdomain
  2. PING myvmi.mysubdomain.default.svc.cluster.local (10.244.0.57) 56(84) bytes of data.
  3. 64 bytes from myvmi.mysubdomain.default.svc.cluster.local (10.244.0.57): icmp_seq=1 ttl=64 time=0.029 ms
  4. [fedora@myvmi ~]$ ip a
  5. 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
  6.     link/ether 0a:58:0a:f4:00:39 brd ff:ff:ff:ff:ff:ff
  7.     inet 10.244.0.57/24 brd 10.244.0.255 scope global dynamic eth0
  8.        valid_lft 86313556sec preferred_lft 86313556sec
  9.     inet6 fe80::858:aff:fef4:39/64 scope link
  10.        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.