Using KubeVirt

Creating a Virtual Machine Image

KubeVirt pulls a containerized image from a container registry to create virtual machine instances. You need to prepare these images before you can use them with KubeVirt. This section contains an example of how to create a container image of Oracle Linux that can be used to create a KubeVirt virtual machine.

This example uses an Oracle Linux cloud image in QCOW format from:

https://yum.oracle.com/oracle-linux-templates.html

For example, on any host that can connect to your local container registry, download the Oracle Linux 9 QCOW image:

wget https://yum.oracle.com/templates/OracleLinux/OL9/u2/x86_64/OL9U2_x86_64-kvm-b197.qcow

Create a Dockerfile so you can load the image into your local container registry. For example, in the same directory as the QCOW image is located, create a file named Dockerfile that contains:

FROM scratch
ADD --chown=107:107 OL9U2_x86_64-kvm-b197.qcow  /disk/

Build a containerized image from the QCOW image. For example:

podman build . -t myregistry.example.com/kubevirt/oraclelinux:ol9.2

You should see output similar to:

STEP 1: FROM scratch
STEP 2: ADD --chown=107:107 OL9U2_x86_64-kvm-b197.qcow  /disk/
STEP 3: COMMIT myregistry.example.com/kubevirt/oraclelinux:ol9.2
--> 09b0b23bb66
Successfully tagged myregistry.example.com/kubevirt/oraclelinux:ol9.2
09b0b23bb6673bdfd1481d81dace0b6008c6ab25e1d156c525b9abaaf8d9f30e

The containerized image is stored locally. You must now upload it to your container registry. If required, log into your container registry:

podman login myregistry.example.com

Push the containerized image to your local registry. For example:

podman push myregistry.example.com/kubevirt/oraclelinux:ol9.2

You should see output similar to:

Getting image source signatures
Copying blob 8a8b1918f588 done  
Copying config 09b0b23bb6 done  
Writing manifest to image destination
Storing signatures

You now have a containerized image for Oracle Linux that you can use to create a KubeVirt virtual machine instance. The container image location in this example is:

myregistry.example.com/kubevirt/oraclelinux:ol9.2

Creating a KubeVirt Instance

This section contains a basic test to verify you can use KubeVirt to create a virtual machine.

This example uses the Oracle Linux 9 container image created in Creating a Virtual Machine Image.

To create a virtual machine with KubeVirt:

Create a VirtualMachine file for your virtual machine. The containerDisk option is where you set the location of the container image to create the virtual machine. This should be the location of a container image in either your local container registry, or a public container registry such as DockerHub. Save the file as vm.yaml.

apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
  name: ol9-no-pvc
spec:
  running: true
  template:
    spec:
      networks:
      - name: foo
        pod: {}
      domain:
        resources:
          requests:
            memory: 1024M
        firmware:
          bootloader: {}
        features:
          smm:
            enabled: true
        devices:
          interfaces:
          - name: foo
            masquerade: {}
            ports:
            - port: 80
          disks:
          - name: containerdisk
            disk:
              bus: virtio
      volumes:
      - name: containerdisk
        containerDisk:
          image: myregistry.example.com/kubevirt/oraclelinux:ol9.2

Create the VirtualMachine:

kubectl apply -f vm.yaml 
virtualmachine.kubevirt.io/ol9-no-pvc created

You can see the VirtualMachine is created using the kubectl get vm command:

kubectl get vm
NAME                           AGE     STATUS    READY
ol9-no-pvc                     28s     Running   True

You can see information on the VirtualMachineInstance using the kubectl get vmi command:

kubectl get vmi
NAME                    AGE   PHASE     IP              NODENAME              READY
ol9-no-pvc              48s   Running   10.244.3.19     worker1.example.com   True

You can get detailed information about the VirtualMachineInstance using the kubectl describe vmi command:

kubectl describe vmi ol9-no-pvc
Name:         ol9-no-pvc
Namespace:    default
Labels:       kubevirt.io/nodeName=worker1.example.com
Annotations:  kubevirt.io/latest-observed-api-version: v1
              kubevirt.io/storage-observed-api-version: v1alpha3
API Version:  kubevirt.io/v1
Kind:         VirtualMachineInstance
...
  Volumes:
    Container Disk:
      Image:              myregistry.example.com/kubevirt/oraclelinux:ol9.2
      Image Pull Policy:  IfNotPresent
    Name:                 containerdisk
...
  Virtual Machine Revision Name:  revision-start-vm-032efda3-040f-4dc0-941d-382daa5f926b-1
  Volume Status:
    Name:    containerdisk
    Target:  sda
Events:
  Type    Reason            Age   From                       Message
  ----    ------            ----  ----                       -------
  Normal  SuccessfulCreate  94s   virtualmachine-controller  Created virtual machine pod virt-launcher-ol9-no-pvc-sz6hb
  Normal  Created           89s   virt-handler               VirtualMachineInstance defined.
  Normal  Started           89s   virt-handler               VirtualMachineInstance started.

You can see the pod that is running that maps to the VirtualMachineInstance using:

kubectl get pod
NAME                             READY   STATUS    RESTARTS   AGE
virt-launcher-ol9-no-pvc-....    2/2     Running   0          1h

You can delete the VirtualMachine using:

kubectl delete vm ol9-no-pvc
virtualmachine.kubevirt.io "ol9-no-pvc" deleted

Creating a KubeVirt Instance with Persistent Storage

This section contains a basic test to verify you can use KubeVirt to create a virtual machine using persistent storage. This type of virtual machine can be live migrated and the state is maintained.

This example uses the Oracle Linux 9 container image created in Creating a Virtual Machine Image.

This example also uses a CephFilesystem that is available via a StorageClass named rook-cephfs. CephFilesystem is a ReadWriteMany filesystem and is useful to allow writing to the virtual machine filesystem to enable state to be maintained and persist over reboots and live migration. Information on setting up a CephFilesystem using the Rook module is available in Rook Module.

To create a virtual machine that uses persistent storage with KubeVirt:

Create a Kubernetes PersistentVolumeClaim file for your StorageClass. In this example, this is a CephFilesystem StorageClass named rook-cephfs. On a control plane node, create a file named pvc-vm.yaml. Copy the following into the file.
```
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: ol9-migratable
spec:
  storageClassName: rook-cephfs
  accessModes:
  - ReadWriteMany
  resources:
    requests:
      storage: 30Gi
```

Create the Kubernetes PersistentVolumeClaim.

kubectl apply -f pvc-vm.yaml
persistentvolumeclaim/ol9-migratable created

Create a VirtualMachine file for your virtual machine. This example uses the PersistentVolumeClaim to enable writing to the virtual machine to maintain state. The containerDisk option is where you set the location of the container image to create the virtual machine. This should be the location of a container image in either your local container registry, or a public container registry such as DockerHub. Save the file as vm.yaml.

apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
  name: ol9
spec:
  running: true
  template:
    spec:
      evictionStrategy: LiveMigrate
      terminationGracePeriodSeconds: 30
      networks:
      - name: foo
        pod: {}
      domain:
        resources:
          requests:
            memory: 1024M
        firmware:
          bootloader: {}
        features:
          smm:
            enabled: true
        devices:
          interfaces:
          - name: foo
            masquerade: {}
            ports:
            - port: 80
          disks:
          - name: containerdisk
            disk:
              bus: virtio
          - name: installdisk
            disk:
              bus: virtio
      volumes:
      - name: containerdisk
        containerDisk:
          image: myregistry.example.com/kubevirt/oraclelinux:ol9.2
      - name: installdisk
        persistentVolumeClaim:
          claimName: ol9-migratable