Instance types and preferences on OpenShift Virtualization Training

Introduction

Mon, 01 Jan 0001 00:00:00 +0000

Even if OpenShift Virtualization 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, OpenShift Virtualization 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.

Common instance types and preferences

Mon, 01 Jan 0001 00:00:00 +0000

The OpenShift Virtualization project provides a set of common instance types and preferences . In this lab, we are going to have a look at these and how they can help us create virtual machines.

Common instance types and preferences

By default OpenShift Virtualization comes with a set of common instance types and preferences. You can reference those instance types and preferences when creating virtual machines.

The cluster provided as well as the user provided instance types and preferences can either be displayed in the web console or by cli.

Create an instance type

Mon, 01 Jan 0001 00:00:00 +0000

In this section, we will create and use our own instance type.

Task 3.3.1: Create your own instance type

In the previous section we have seen that the Cirros preference requests 256Mi of memory. However, the smallest instance type available requests 512Mi of memory. In order to adapt to this, let’s create our own instance type and assign it to our VirtualMachines.

Define the following instance type:

Request 256Mi of memory
Reduce the overcommit percentage from 50% to 25%
Name the resource lab03-o1-pico

Task hint

Create the following resource using the import YAML functionality of the OpenShift Web Console:

Re-assign an instance type

Mon, 01 Jan 0001 00:00:00 +0000

In this section we will change the instance type of our running VMs to our newly created instance type.

Changing an instance type

Whenever a VM referencing an instance type or preference is created, the definition at time of creation is stored in a ControllerRevision. This revision is then referenced in a new field .spec.instancetype.revisionName in our VM manifest.

This field ensures that our VirtualMachine knows the original specification even when the type or preference would change. This ensures that there are no accidental changes to the VM resources or preferences.