Templates

!!! Note By deploying KubeVirt on top of OpenShift the user can benefit from the OpenShift Template functionality.

Virtual machine templates

What is a virtual machine template?

The KubeVirt projects provides a set of templates to create VMs to handle common usage scenarios. These templates provide a combination of some key factors that could be further customized and processed to have a Virtual Machine object. The key factors which define a template are

Workload Most Virtual Machine should be server or desktop to have maximum flexibility; the highperformance workload trades some of this flexibility to provide better performances.
Guest Operating System (OS) This allow to ensure that the emulated hardware is compatible with the guest OS. Furthermore, it allows to maximize the stability of the VM, and allows performance optimizations.
Size (flavor) Defines the amount of resources (CPU, memory) to allocate to the VM.

More documentation is available in the common templates subproject

Accessing the virtual machine templates

If you installed KubeVirt using a supported method you should find the common templates preinstalled in the cluster. Should you want to upgrade the templates, or install them from scratch, you can use one of the supported releases

To install the templates:

    $ export VERSION=$(curl -s https://api.github.com/repos/kubevirt/common-templates/releases | grep tag_name | grep -v -- '-rc' | head -1 | awk -F': ' '{print $2}' | sed 's/,//' | xargs)
    $ oc create -f https://github.com/kubevirt/common-templates/releases/download/$VERSION/common-templates-$VERSION.yaml

Editable fields

You can edit the fields of the templates which define the amount of resources which the VMs will receive.

Each template can list a different set of fields that are to be considered editable. The fields are used as hints for the user interface, and also for other components in the cluster.

The editable fields are taken from annotations in the template. Here is a snippet presenting a couple of most commonly found editable fields:

    metadata:
      annotations:
        template.kubevirt.io/editable: |
          /objects[0].spec.template.spec.domain.cpu.sockets
          /objects[0].spec.template.spec.domain.cpu.cores
          /objects[0].spec.template.spec.domain.cpu.threads
          /objects[0].spec.template.spec.domain.resources.requests.memory

Each entry in the editable field list must be a jsonpath. The jsonpath root is the objects: element of the template. The actually editable field is the last entry (the "leaf") of the path. For example, the following minimal snippet highlights the fields which you can edit:

    objects:
      spec:
        template:
          spec:
            domain:
              cpu:
                sockets:
                  VALUE # this is editable
                cores:
                  VALUE # this is editable
                threads:
                  VALUE # this is editable
              resources:
                requests:
                  memory:
                    VALUE # this is editable

Relationship between templates and VMs

Once processed the templates produce VM objects to be used in the cluster. The VMs produced from templates will have a vm.kubevirt.io/template label, whose value will be the name of the parent template, for example fedora-desktop-medium:

      metadata:
        labels:
          vm.kubevirt.io/template: fedora-desktop-medium

In addition, these VMs can include an optional label vm.kubevirt.io/template-namespace, whose value will be the namespace of the parent template, for example:

      metadata:
        labels:
          vm.kubevirt.io/template-namespace: openshift

If this label is not defined, the template is expected to belong to the same namespace as the VM.

This make it possible to query for all the VMs built from any template.

Example:

    oc process -o yaml -f dist/templates/rhel8-server-tiny.yaml NAME=rheltinyvm SRC_PVC_NAME=rhel SRC_PVC_NAMESPACE=kubevirt

And the output:

    apiVersion: v1
    items:
    - apiVersion: kubevirt.io/v1alpha3
      kind: VirtualMachine
      metadata:
        annotations:
          vm.kubevirt.io/flavor: tiny
          vm.kubevirt.io/os: rhel8
          vm.kubevirt.io/validations: |
            [
              {
                "name": "minimal-required-memory",
                "path": "jsonpath::.spec.domain.resources.requests.memory",
                "rule": "integer",
                "message": "This VM requires more memory.",
                "min": 1610612736
              }
            ]
          vm.kubevirt.io/workload: server
        labels:
          app: rheltinyvm
          vm.kubevirt.io/template: rhel8-server-tiny
          vm.kubevirt.io/template.revision: "45"
          vm.kubevirt.io/template.version: 0.11.3
        name: rheltinyvm
      spec:
        dataVolumeTemplates:
        - apiVersion: cdi.kubevirt.io/v1beta1
          kind: DataVolume
          metadata:
            name: rheltinyvm
          spec:
            pvc:
              accessModes:
              - ReadWriteMany
              resources:
                requests:
                  storage: 30Gi
            source:
              pvc:
                name: rhel
                namespace: kubevirt
        running: false
        template:
          metadata:
            labels:
              kubevirt.io/domain: rheltinyvm
              kubevirt.io/size: tiny
          spec:
            domain:
              cpu:
                cores: 1
                sockets: 1
                threads: 1
              devices:
                disks:
                - disk:
                    bus: virtio
                  name: rheltinyvm
                - disk:
                    bus: virtio
                  name: cloudinitdisk
                interfaces:
                - masquerade: {}
                  name: default
                networkInterfaceMultiqueue: true
                rng: {}
              resources:
                requests:
                  memory: 1.5Gi
            networks:
            - name: default
              pod: {}
            terminationGracePeriodSeconds: 180
            volumes:
            - dataVolume:
                name: rheltinyvm
              name: rheltinyvm
            - cloudInitNoCloud:
                userData: |-
                  #cloud-config
                  user: cloud-user
                  password: lymp-fda4-m1cv
                  chpasswd: { expire: False }
              name: cloudinitdisk
    kind: List
    metadata: {}

You can add the VM from the template to the cluster in one go

    oc process rhel8-server-tiny NAME=rheltinyvm SRC_PVC_NAME=rhel SRC_PVC_NAMESPACE=kubevirt | oc apply -f -

Please note that after the generation step VM and template objects have no relationship with each other besides the aforementioned label. Changes in templates do not automatically affect VMs or vice versa.

common template customization

The templates provided by the kubevirt project provide a set of conventions and annotations that augment the basic feature of the openshift templates. You can customize your kubevirt-provided templates editing these annotations, or you can add them to your existing templates to make them consumable by the kubevirt services.

Here's a description of the kubevirt annotations. Unless otherwise specified, the following keys are meant to be top-level entries of the template metadata, like

    apiVersion: v1
    kind: Template
    metadata:
      name: windows-10
      annotations:
        openshift.io/display-name: "Generic demo template"

All the following annotations are prefixed with defaults.template.kubevirt.io, which is omitted below for brevity. So the actual annotations you should use will look like

    apiVersion: v1
    kind: Template
    metadata:
      name: windows-10
      annotations:
        defaults.template.kubevirt.io/disk: default-disk
        defaults.template.kubevirt.io/volume: default-volume
        defaults.template.kubevirt.io/nic: default-nic
        defaults.template.kubevirt.io/network: default-network

Unless otherwise specified, all annotations are meant to be safe defaults, both for performance and compatibility, and hints for the CNV-aware UI and tooling.

disk

See the section references below.

Example:

    apiVersion: v1
    kind: Template
    metadata:
      name: Linux
      annotations:
        defaults.template.kubevirt.io/disk: rhel-disk

nic

See the section references below.

Example:

    apiVersion: v1
    kind: Template
    metadata:
      name: Windows
      annotations:
        defaults.template.kubevirt.io/nic: my-nic

volume

See the section references below.

Example:

    apiVersion: v1
    kind: Template
    metadata:
      name: Linux
      annotations:
        defaults.template.kubevirt.io/volume: custom-volume

network

See the section references below.

Example:

    apiVersion: v1
    kind: Template
    metadata:
      name: Linux
      annotations:
        defaults.template.kubevirt.io/network: fast-net

references

The default values for network, nic, volume, disk are meant to be the name of a section later in the document that the UI will find and consume to find the default values for the corresponding types. For example, considering the annotation defaults.template.kubevirt.io/disk: my-disk: we assume that later in the document it exists an element called my-disk that the UI can use to find the data it needs. The names actually don't matter as long as they are legal for kubernetes and consistent with the content of the document.

complete example

demo-template.yaml

apiversion: v1
items:
- apiversion: kubevirt.io/v1alpha3
  kind: virtualmachine
  metadata:
    labels:
      vm.kubevirt.io/template: rhel7-generic-tiny
    name: rheltinyvm
    osinfoname: rhel7.0
    defaults.template.kubevirt.io/disk: rhel-default-disk
    defaults.template.kubevirt.io/nic: rhel-default-net
  spec:
    running: false
    template:
      spec:
        domain:
          cpu:
            sockets: 1
            cores: 1
            threads: 1
          devices:
            rng: {}
          resources:
            requests:
              memory: 1g
        terminationgraceperiodseconds: 0
        volumes:
        - containerDisk:
          image: registry:5000/kubevirt/cirros-container-disk-demo:devel
          name: rhel-default-disk
        networks:
        - genie:
          networkName: flannel
          name: rhel-default-net
kind: list
metadata: {}

once processed becomes: demo-vm.yaml

apiVersion: kubevirt.io/v1alpha3
kind: VirtualMachine
metadata:
  labels:
    vm.kubevirt.io/template: rhel7-generic-tiny
  name: rheltinyvm
  osinfoname: rhel7.0
spec:
  running: false
  template:
    spec:
      domain:
        cpu:
          sockets: 1
          cores: 1
          threads: 1
        resources:
          requests:
            memory: 1g
        devices:
          rng: {}
          disks:
          - disk:
            name: rhel-default-disk
        interfaces:
        - bridge: {}
          name: rhel-default-nic
      terminationgraceperiodseconds: 0
      volumes:
      - containerDisk:
          image: registry:5000/kubevirt/cirros-container-disk-demo:devel
        name: containerdisk
      networks:
      - genie:
          networkName: flannel
        name: rhel-default-nic

Virtual machine creation

Overview

The key factors which define a template are - Workload Most Virtual Machine should be server or desktop to have maximum flexibility; the highperformance workload trades some of this flexibility to provide better performances. - Guest Operating System (OS) This allow to ensure that the emulated hardware is compatible with the guest OS. Furthermore, it allows to maximize the stability of the VM, and allows performance optimizations. - Size (flavor) Defines the amount of resources (CPU, memory) to allocate to the VM.

Openshift Console

VMs can be created through OpenShift Cluster Console UI . This UI supports creation VM using templates and templates features - flavors and workload profiles. To create VM from template, choose WorkLoads in the left panel >> choose Virtualization >> press to the "Create Virtual Machine" blue button >> choose "Create from wizard". Next, you have to see "Create Virtual Machine" window

Common-templates

There is the common-templates subproject. It provides official prepared and useful templates. You can also create templates by hand. You can find an example below, in the "Example template" section.

Example template

In order to create a virtual machine via OpenShift CLI, you need to provide a template defining the corresponding object and its metadata.

NOTE Only VirtualMachine object is currently supported.

Here is an example template that defines an instance of the VirtualMachine object:

apiVersion: template.openshift.io/v1
kind: Template
metadata:
  name: fedora-desktop-large
  annotations:
    openshift.io/display-name: "Fedora 32+ VM"
    description: >-
      Template for Fedora 32 VM or newer.
      A PVC with the Fedora disk image must be available.
      Recommended disk image:
      https://download.fedoraproject.org/pub/fedora/linux/releases/32/Cloud/x86_64/images/Fedora-Cloud-Base-32-1.6.x86_64.qcow2
    tags: "hidden,kubevirt,virtualmachine,fedora"
    iconClass: "icon-fedora"
    openshift.io/provider-display-name: "KubeVirt"
    openshift.io/documentation-url: "https://github.com/kubevirt/common-templates"
    openshift.io/support-url: "https://github.com/kubevirt/common-templates/issues"
    template.openshift.io/bindable: "false"
    template.kubevirt.io/version: v1alpha1
    defaults.template.kubevirt.io/disk: rootdisk
    template.kubevirt.io/editable: |
      /objects[0].spec.template.spec.domain.cpu.sockets
      /objects[0].spec.template.spec.domain.cpu.cores
      /objects[0].spec.template.spec.domain.cpu.threads
      /objects[0].spec.template.spec.domain.resources.requests.memory
      /objects[0].spec.template.spec.domain.devices.disks
      /objects[0].spec.template.spec.volumes
      /objects[0].spec.template.spec.networks
    name.os.template.kubevirt.io/fedora32: Fedora 32 or higher
    name.os.template.kubevirt.io/fedora33: Fedora 32 or higher
    name.os.template.kubevirt.io/silverblue32: Fedora 32 or higher
    name.os.template.kubevirt.io/silverblue33: Fedora 32 or higher
  labels:
    os.template.kubevirt.io/fedora32: "true"
    os.template.kubevirt.io/fedora33: "true"
    os.template.kubevirt.io/silverblue32: "true"
    os.template.kubevirt.io/silverblue33: "true"
    workload.template.kubevirt.io/desktop: "true"
    flavor.template.kubevirt.io/large: "true"
    template.kubevirt.io/type: "base"
    template.kubevirt.io/version: "0.11.3"
objects:
- apiVersion: kubevirt.io/v1alpha3
  kind: VirtualMachine
  metadata:
    name: ${NAME}
    labels:
      vm.kubevirt.io/template: fedora-desktop-large
      vm.kubevirt.io/template.version: "0.11.3"
      vm.kubevirt.io/template.revision: "45"
      app: ${NAME}
    annotations:
      vm.kubevirt.io/os: "fedora"
      vm.kubevirt.io/workload: "desktop"
      vm.kubevirt.io/flavor: "large"
      vm.kubevirt.io/validations: |
        [
          {
            "name": "minimal-required-memory",
            "path": "jsonpath::.spec.domain.resources.requests.memory",
            "rule": "integer",
            "message": "This VM requires more memory.",
            "min": 1073741824
          }
        ]
  spec:
    dataVolumeTemplates:
    - apiVersion: cdi.kubevirt.io/v1beta1
      kind: DataVolume
      metadata:
        name: ${NAME}
      spec:
        pvc:
          accessModes:
            - ReadWriteMany
          resources:
            requests:
              storage: 30Gi
        source:
          pvc:
            name: ${SRC_PVC_NAME}
            namespace: ${SRC_PVC_NAMESPACE}
    running: false
    template:
      metadata:
        labels:
          kubevirt.io/domain: ${NAME}
          kubevirt.io/size: large
      spec:
        domain:
          cpu:
            sockets: 2
            cores: 1
            threads: 1
          resources:
            requests:
              memory: 8Gi
          devices:
            rng: {}
            networkInterfaceMultiqueue: true
            inputs:
              - type: tablet
                bus: virtio
                name: tablet
            disks:
            - disk:
                bus: virtio
              name: ${NAME}
            - disk:
                bus: virtio
              name: cloudinitdisk
            interfaces:
            - masquerade: {}
              name: default
        terminationGracePeriodSeconds: 180
        networks:
        - name: default
          pod: {}
        volumes:
        - dataVolume:
            name: ${NAME}
          name: ${NAME}
        - cloudInitNoCloud:
            userData: |-
              #cloud-config
              user: fedora
              password: ${CLOUD_USER_PASSWORD}
              chpasswd: { expire: False }
          name: cloudinitdisk
parameters:
- description: VM name
  from: 'fedora-[a-z0-9]{16}'
  generate: expression
  name: NAME
- name: SRC_PVC_NAME
  description: Name of the PVC to clone
  value: 'fedora'
- name: SRC_PVC_NAMESPACE
  description: Namespace of the source PVC
  value: kubevirt-os-images
- description: Randomized password for the cloud-init user fedora
  from: '[a-z0-9]{4}-[a-z0-9]{4}-[a-z0-9]{4}'
  generate: expression
  name: CLOUD_USER_PASSWORD

Note that the template above defines free parameters (NAME, SRC_PVC_NAME, SRC_PVC_NAMESPACE, CLOUD_USER_PASSWORD) and the NAME parameter does not have specified default value.

An OpenShift template has to be converted into the JSON file via oc process command, that also allows you to set the template parameters.

A complete example can be found in the KubeVirt repository.

!> You need to be logged in by oc login command.

$ oc process -f cluster/vmi-template-fedora.yaml\
    -p NAME=testvmi \
    -p SRC_PVC_NAME=fedora \
    -p SRC_PVC_NAMESPACE=kubevirt \
{
    "kind": "List",
    "apiVersion": "v1",
    "metadata": {},
    "items": [
        {

The JSON file is usually applied directly by piping the processed output to oc create command.

$ oc process -f cluster/examples/vm-template-fedora.yaml \
    -p NAME=testvm \
    -p SRC_PVC_NAME=fedora \
    -p SRC_PVC_NAMESPACE=kubevirt \
    | oc create -f -
virtualmachine.kubevirt.io/testvm created

The command above results in creating a Kubernetes object according to the specification given by the template \(in this example it is an instance of the VirtualMachine object\).

It's possible to get list of available parameters using the following command:

$ oc process -f dist/templates/fedora-desktop-large.yaml --parameters
NAME                  DESCRIPTION                                          GENERATOR           VALUE
NAME                  VM name                                              expression          fedora-[a-z0-9]{16}
SRC_PVC_NAME          Name of the PVC to clone                                                 fedora
SRC_PVC_NAMESPACE     Namespace of the source PVC                                              kubevirt-os-images
CLOUD_USER_PASSWORD   Randomized password for the cloud-init user fedora   expression          [a-z0-9]{4}-[a-z0-9]{4}-[a-z0-9]{4}

Starting virtual machine from the created object

The created object is now a regular VirtualMachine object and from now it can be controlled by accessing Kubernetes API resources. The preferred way how to do this from within the OpenShift environment is to use oc patch command.

$ oc patch virtualmachine testvm --type merge -p '{"spec":{"running":true}}'
virtualmachine.kubevirt.io/testvm patched

Do not forget about virtctl tool. Using it in the real cases instead of using kubernetes API can be more convenient. Example:

$ virtctl start testvm
VM testvm was scheduled to start

As soon as VM starts, Kubernetes creates new type of object - VirtualMachineInstance. It has similar name to VirtualMachine. Example (not full output, it's too big):

$ kubectl describe vm testvm
name:         testvm
Namespace:    myproject
Labels:       kubevirt-vm=vm-testvm
              kubevirt.io/os=fedora33
Annotations:  <none>
API Version:  kubevirt.io/v1alpha3
Kind:         VirtualMachine

Cloud-init script and parameters

Kubevirt VM templates, just like kubevirt VM/VMI yaml configs, supports cloud-init scripts

Hack - use pre-downloaded image

Kubevirt VM templates, just like kubevirt VM/VMI yaml configs, can use pre-downloaded VM image, which can be a useful feature especially in the debug/development/testing cases. No special parameters required in the VM template or VM/VMI yaml config. The main idea is to create Kubernetes PersistentVolume and PersistentVolumeClaim corresponding to existing image in the file system. Example:

---
kind: PersistentVolume
apiVersion: v1
metadata:
  name: mypv
  labels:
    type: local
spec:
  storageClassName: manual
  capacity:
    storage: 10G
  accessModes:
    - ReadWriteOnce
  hostPath:
    path: "/mnt/sda1/images/testvm"
---
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: mypvc
spec:
  storageClassName: manual
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 10G

Using DataVolumes

Kubevirt VM templates are using dataVolumeTemplates. Before using dataVolumes, CDI has to be installed in cluster. After that, source Datavolume can be created.

---
apiVersion: cdi.kubevirt.io/v1beta1
kind: DataVolume
metadata:
  name: fedora-datavolume-original
  namespace: kubevirt
spec:
  source:
    registry:
      url: "image_url"
  pvc:
    accessModes:
      - ReadWriteOnce
    resources:
      requests:
        storage: 30Gi

After import is completed, VM can be created:

$ oc process -f cluster/examples/vm-template-fedora.yaml \
    -p NAME=testvmi \
    -p SRC_PVC_NAME=fedora-datavolume-original \
    -p SRC_PVC_NAMESPACE=kubevirt \
    | oc create -f -
virtualmachine.kubevirt.io/testvm created

Additional information

You can follow Virtual Machine Lifecycle Guide for further reference.

PreviousRun Strategies NextWindows virtio drivers

Last updated 3 years ago