Creating VMs from instance types - Creating a virtual machine | Virtualization

About instance types
- Required attributes
- Optional attributes
Pre-defined instance types

You can simplify virtual machine (VM) creation by using instance types, whether you use the OKD web console or the CLI to create VMs.

About instance types

An instance type is a reusable object where you can define resources and characteristics to apply to new VMs. You can define custom instance types or use the variety that are included when you install OKD Virtualization.

To create a new instance type, you must first create a manifest, either manually or by using the virtctl CLI tool. You then create the instance type object by applying the manifest to your cluster.

OKD Virtualization provides two CRDs for configuring instance types:

A namespaced object: VirtualMachineInstancetype
A cluster-wide object: VirtualMachineClusterInstancetype

These objects use the same VirtualMachineInstancetypeSpec.

Required attributes

When you configure an instance type, you must define the cpu and memory attributes. Other attributes are optional.

When you create a VM from an instance type, you cannot override any parameters defined in the instance type.

Because instance types require defined CPU and memory attributes, OKD Virtualization always rejects additional requests for these resources when creating a VM from an instance type.

You can manually create an instance type manifest. For example:

Example YAML file with required fields

apiVersion: instancetype.kubevirt.io/v1beta1
kind: VirtualMachineInstancetype
metadata:
  name: example-instancetype
spec:
  cpu:
    guest: 1 (1)
  memory:
    guest: 128Mi (2)

1	Required. Specifies the number of vCPUs to allocate to the guest.
2	Required. Specifies an amount of memory to allocate to the guest.

You can create an instance type manifest by using the virtctl CLI utility. For example:

Example virtctl command with required fields

$ virtctl create instancetype --cpu 2 --memory 256Mi

where:

--cpu <value>: Specifies the number of vCPUs to allocate to the guest. Required.
--memory <value>: Specifies an amount of memory to allocate to the guest. Required.

You can immediately create the object from the new manifest by running the following command:

$ virtctl create instancetype --cpu 2 --memory 256Mi | oc apply -f -

Optional attributes

In addition to the required cpu and memory attributes, you can include the following optional attributes in the VirtualMachineInstancetypeSpec:

annotations: List annotations to apply to the VM.
gpus: List vGPUs for passthrough.
hostDevices: List host devices for passthrough.
ioThreadsPolicy: Define an IO threads policy for managing dedicated disk access.
launchSecurity: Configure Secure Encrypted Virtualization (SEV).
nodeSelector: Specify node selectors to control the nodes where this VM is scheduled.
schedulerName: Define a custom scheduler to use for this VM instead of the default scheduler.

Pre-defined instance types

OKD Virtualization includes a set of pre-defined instance types called common-instancetypes. Some are specialized for specific workloads and others are workload-agnostic.

These instance type resources are named according to their series, version, and size. The size value follows the . delimiter and ranges from nano to 8xlarge.

Table 1. `common-instancetypes` series comparison
Use case	Series	Characteristics	vCPU to memory ratio	Example resource
Universal	U	Burstable CPU performance	1:4	`u1.medium` 1 vCPUs 4 Gi memory
Overcommitted	O	Overcommitted memory Burstable CPU performance	1:4	`o1.small` 1 vCPU 2Gi memory
Compute-exclusive	CX	Hugepages Dedicated CPU Isolated emulator threads vNUMA	1:2	`cx1.2xlarge` 8 vCPUs 16Gi memory
NVIDIA GPU	GN	For VMs that use GPUs provided by the NVIDIA GPU Operator Has predefined GPUs Burstable CPU performance	1:4	`gn1.8xlarge` 32 vCPUs 128Gi memory
Memory-intensive	M	Hugepages Burstable CPU performance	1:8	`m1.large` 2 vCPUs 16Gi memory
Network-intensive	N	Hugepages Dedicated CPU Isolated emulator threads Requires nodes capable of running DPDK workloads	1:2	`n1.medium` 4 vCPUs 4Gi memory

Creating virtual machines from instance types

About instance types

Required attributes

Optional attributes

Pre-defined instance types