3.1. Introduction

Use your own instance type

Even if KubeVirt provides advanced options and a lot of configuration options for different VMs, we usually have a common set of VM specifications which we will use for most of our VMs. Therefore, it may make sense to define such specifications as instance types and / or preferences.

To achieve this, KubeVirt provides multiple CustomResourceDefinitions like VirtualMachineInstancetype, VirtualMachineClusterInstancetype or VirtualMachinePreference.

VM VirtualMachineInstancetype

For an instance type we have the option of using the cluster-wide VirtualMachineClusterInstancetype or the namespaced VirtualMachineInstancetype.

With instance types we can define the following resource-related characteristics:

CPU - Required number of vCPUs presented to the guest
Memory - Required amount of memory presented to the guest
GPUs - Optional list of vGPUs to passthrough
HostDevices - Optional list of HostDevices to pass through
IOThreadsPolicy - Optional IOThreadsPolicy to be used
LaunchSecurity - Optional LaunchSecurity to be used

Important

Any provided instance type characteristic can not be overridden from within the VirtualMachine. Be aware that CPU and Memory both are required for an instance type. Therefore, any different request of CPU or Memory on a VirtualMachine resource will conflict and the request will be rejected.

VM preference

KubeVirt also provides a CRD VirtualMachineClusterPreference for cluster-wide preferences as well as a namespaced version VirtualMachinePreference. A preference specification encapsulates every value of the remaining attributes of a VirtualMachine.

Note

Unlike the characteristics from an instance type, the preferences only define the preferred values. They can be overridden in the VirtualMachine specification. The specification from the VirtualMachine has priority.

Using instance type or preference in a virtual machine

A sample virtual machine referencing an instance type and preference looks like this:

apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
  name: lab03-examplevm
spec:
  instancetype:
    kind: VirtualMachineInstancetype
    name: lab03-example-instancetype
  preference:
    kind: VirtualMachinePreference
    name: lab03-example-preference