virt-template

A KubeVirt add-on providing native, user-friendly templating workflows for KubeVirt virtual machines.

Quick Example

cat <<'EOF' | kubectl apply -f -
apiVersion: template.kubevirt.io/v1alpha1
kind: VirtualMachineTemplate
metadata:
  name: fedora
spec:
  parameters:
    - name: NAME
      required: true
    - name: INSTANCETYPE
      value: u1.medium
    - name: PREFERENCE
      value: fedora
  virtualMachine:
    metadata:
      name: ${NAME}
    spec:
      runStrategy: Always
      instancetype:
        name: ${INSTANCETYPE}
      preference:
        name: ${PREFERENCE}
      template:
        spec:
          domain:
            devices: {}
          terminationGracePeriodSeconds: 180
          volumes:
            - containerDisk:
                image: quay.io/containerdisks/fedora:latest
              name: containerdisk-0
            - cloudInitNoCloud:
                userData: |
                  #cloud-config
                  password: fedora
                  chpasswd: { expire: False }
                  ssh_pwauth: True
              name: cloudinitdisk-0
EOF

# Process and create a VM
virttemplatectl process fedora -p NAME=my-fedora --create

Description

virt-template enables users to create, share, and manage VM blueprints directly within the cluster. The project provides native support for in-cluster templating through the VirtualMachineTemplate custom resource, which allows you to define reusable VM templates with configurable parameters that can be substituted at runtime to create VirtualMachine instances.

Developed as a separate operator outside core KubeVirt, virt-template is influenced by OpenShift's Template CRD and designed to provide a more traditional virtualization experience within Kubernetes.

Components

• virt-template-controller: Kubernetes controller that watches and validates VirtualMachineTemplate resources
• virt-template-apiserver: API server providing subresource APIs for templates
• virttemplatectl: CLI tool for local template processing and management

Key Features

• VM Blueprints: Create reusable VM templates with parameter placeholders using ${NAME} syntax
• Parameter Substitution: Define static values, generated values, or required parameters for flexible template instantiation
• Server-Side Processing: Process templates in-cluster via the process subresource API
• Cross-Namespace Sharing: Share and reuse templates across namespaces within your cluster

Getting Started

Prerequisites

For development:

• Go version v1.24.0+
• Container tool: Podman (default) or Docker
• kubectl

For deployment on Kubernetes:

• cert-manager installed in the cluster
• KubeVirt installed in the cluster

For deployment on OpenShift:

• OpenShift Virtualization installed in the cluster

Development

Build binaries locally:

make build              # Build controller binary
make build-apiserver    # Build apiserver binary
make build-virttemplatectl  # Build CLI tool

Run linting and formatting:

make fmt vet lint

Run unit tests:

make test

Deployment

Quick Start with kubevirtci

The easiest way to develop and test is using kubevirtci:

make cluster-up        # Start local KubeVirt cluster
make cluster-sync      # Build, push, and deploy to cluster
make cluster-functest  # Run functional tests
make cluster-down      # Stop cluster

Manual Deployment

virt-template supports two deployment configurations:

• config/default - Standard Kubernetes deployment (requires cert-manager)
• config/openshift - OpenShift deployment (uses built-in Service CA operator)

Build and push container images:

make container-build container-push \
  IMG_REGISTRY=<registry> \
  IMG_TAG=<tag>

The build supports multi-arch images (amd64, arm64, s390x). Use CONTAINER_TOOL=docker or CONTAINER_TOOL=podman.

Deploy on Kubernetes:

make install
make deploy IMG_REGISTRY=<registry> IMG_TAG=<tag>

Deploy on OpenShift:

make install
make deploy-openshift IMG_REGISTRY=<registry> IMG_TAG=<tag>

Create a sample VirtualMachineTemplate:

kubectl apply -f config/samples/template_v1alpha1_virtualmachinetemplate.yaml

Uninstall

Uninstall from Kubernetes:

kubectl delete vmt --all  # Delete sample instances
make undeploy             # Remove controllers
make uninstall            # Remove CRDs

Uninstall from OpenShift:

kubectl delete vmt --all     # Delete sample instances
make undeploy-openshift      # Remove controllers
make uninstall               # Remove CRDs

Using virttemplatectl

Process a template locally:

virttemplatectl process -f template.yaml -p NAME=myvm -p INSTANCETYPE=u1.small

Convert OpenShift templates to VirtualMachineTemplate:

virttemplatectl convert -f openshift-template.yaml

Usage

VirtualMachineTemplate CRD

The VirtualMachineTemplate custom resource allows you to define reusable VM blueprints with parameters:

apiVersion: template.kubevirt.io/v1alpha1
kind: VirtualMachineTemplate
metadata:
  name: my-template
spec:
  parameters:
    - name: NAME
      description: Name of the VM
      required: true
    - name: MEMORY
      description: Memory size
      value: "2Gi"
    - name: PASSWORD
      generate: expression
      from: "[a-zA-Z0-9]{16}"
  virtualMachine:
    metadata:
      name: ${NAME}
[...]

Parameter Substitution

Parameters are referenced using ${PARAMETER_NAME} syntax. They can have:

• Static values: Pre-defined default values (value: "2Gi")
• Generated values: Random values from expression generator
• Required flag: Mark parameters as mandatory (required: true)

Parameter Generation

The expression generator creates random values using regex-like syntax:

parameters:
  - name: PASSWORD
    generate: expression
    from: "[a-zA-Z0-9]{16}"  # Generates 16 random alphanumeric chars
  - name: API_KEY
    generate: expression
    from: "[A-F0-9]{32}"      # Generates 32 random hex chars (uppercase)

Supported character classes:

• [a-z] - lowercase letters
• [A-Z] - uppercase letters
• [0-9] - digits
• [a-zA-Z0-9] - alphanumeric
• \w - word characters (letters, digits, underscore)
• \d - digits
• \a - alphabetic characters
• \A - special characters

Processing Templates

Process VirtualMachineTemplate via API:

virttemplatectl process my-template \
  -p NAME=myvm \
  -p MEMORY=4Gi

Process VirtualMachineTemplate and create VirtualMachine via API:

virttemplatectl process my-template \
  -p NAME=myvm \
  -p MEMORY=4Gi \
  --create

Process local template file:

virttemplatectl process -f my-template.yaml \
  -p NAME=myvm \
  -p MEMORY=4Gi

Process from stdin:

cat my-template.yaml | virttemplatectl process -f - \
  -p NAME=myvm \
  -p MEMORY=4Gi

Distribution

Build Installer Bundle

Generate a single YAML file with all resources:

For Kubernetes:

make build-installer IMG_REGISTRY=<registry> IMG_TAG=<tag>

This creates dist/install.yaml which can be deployed with:

kubectl apply -f dist/install.yaml

For OpenShift:

make build-installer-openshift IMG_REGISTRY=<registry> IMG_TAG=<tag>

This creates dist/install-openshift.yaml which can be deployed with:

kubectl apply -f dist/install-openshift.yaml

Development Tools

Run make help to see all available make targets.

Kubevirtci workflows:

The project provides two kubevirtci-based development environments:

• cluster-* targets: Test with a stable KubeVirt release
• kubevirt-* targets: Test with KubeVirt from git main

Example workflow:

make cluster-up        # Start kubevirtci cluster
make cluster-sync      # Build, deploy, and test
make cluster-functest  # Run functional tests
make cluster-down      # Stop cluster

Contributing

Contributions are welcome! Please ensure:

• All tests pass: make test functest
• make all passes (runs formatting, vetting, linting, and code generation)

License

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

Copyright The KubeVirt Authors.