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92 lines
3.7 KiB
Plaintext
92 lines
3.7 KiB
Plaintext
// Module included in the following assemblies:
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//
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// * virt/virtual_machines/creating_vm/virt-creating-vms-from-instance-types.adoc
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:_mod-docs-content-type: CONCEPT
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[id="virt-about-instance-types_{context}"]
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= About instance types
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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 {VirtProductName}.
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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.
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{VirtProductName} provides two CRDs for configuring instance types:
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* A namespaced object: `VirtualMachineInstancetype`
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* A cluster-wide object: `VirtualMachineClusterInstancetype`
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These objects use the same `VirtualMachineInstancetypeSpec`.
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[id="required-attributes_{context}"]
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== Required attributes
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When you configure an instance type, you must define the `cpu` and `memory` attributes. Other attributes are optional.
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[NOTE]
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====
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When you create a VM from an instance type, you cannot override any parameters defined in the instance type.
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Because instance types require defined CPU and memory attributes, {VirtProductName} always rejects additional requests for these resources when creating a VM from an instance type.
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====
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You can manually create an instance type manifest. For example:
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.Example YAML file with required fields
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[source,yaml]
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----
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apiVersion: instancetype.kubevirt.io/v1beta1
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kind: VirtualMachineInstancetype
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metadata:
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name: example-instancetype
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spec:
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cpu:
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guest: 1 <1>
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memory:
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guest: 128Mi <2>
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----
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<1> Required. Specifies the number of vCPUs to allocate to the guest.
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<2> Required. Specifies an amount of memory to allocate to the guest.
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You can create an instance type manifest by using the `virtctl` CLI utility. For example:
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.Example `virtctl` command with required fields
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[source,terminal]
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----
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$ virtctl create instancetype --cpu 2 --memory 256Mi
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----
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where:
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`--cpu <value>`:: Specifies the number of vCPUs to allocate to the guest. Required.
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`--memory <value>`:: Specifies an amount of memory to allocate to the guest. Required.
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[TIP]
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====
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You can immediately create the object from the new manifest by running the following command:
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[source,terminal]
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----
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$ virtctl create instancetype --cpu 2 --memory 256Mi | oc apply -f -
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----
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====
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[id="optional-attributes_{context}"]
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== Optional attributes
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In addition to the required `cpu` and `memory` attributes, you can include the following optional attributes in the `VirtualMachineInstancetypeSpec`:
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`annotations`:: List annotations to apply to the VM.
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`gpus`:: List vGPUs for passthrough.
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`hostDevices`:: List host devices for passthrough.
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`ioThreadsPolicy`:: Define an IO threads policy for managing dedicated disk access.
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`launchSecurity`:: Configure Secure Encrypted Virtualization (SEV).
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`nodeSelector`:: Specify node selectors to control the nodes where this VM is scheduled.
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`schedulerName`:: Define a custom scheduler to use for this VM instead of the default scheduler.
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[id="virt-about-instance-types-controller-revisions_{context}"]
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== Controller revisions
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When you create a VM by using an instance type, a `ControllerRevision` object retains an immutable snapshot of the instance type object. This snapshot locks in resource-related characteristics defined in the instance type object, such as the required guest CPU and memory. The VM status also contains a reference to the `ControllerRevision` object.
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This snapshot is essential for versioning, and ensures that the VM instance created when starting a VM does not change if the underlying instance type object is updated while the VM is running.
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