openshift-docs/modules/virt-example-vm-node-placement-node-affinity.adoc

// Module included in the following assemblies:
//
// * virt/virtual_machines/advanced_vm_management/virt-specifying-nodes-for-vms.adoc

[id="virt-example-vm-node-placement-node-affinity_{context}"]
= Example: VM node placement with node affinity

In this example, the VM must be scheduled on a node that has the label `example.io/example-key = example-value-1` or the label `example.io/example-key = example-value-2`. The constraint is met if only one of the labels is present on the node. If neither label is present, the VM is not scheduled.

If possible, the scheduler avoids nodes that have the label `example-node-label-key = example-node-label-value`. However, if all candidate nodes have this label, the scheduler ignores this constraint.

.Example VM manifest
[source,yaml]
----
metadata:
  name: example-vm-node-affinity
apiVersion: kubevirt.io/v1
kind: VirtualMachine
spec:
  affinity:
    nodeAffinity:
      requiredDuringSchedulingIgnoredDuringExecution: <1>
        nodeSelectorTerms:
        - matchExpressions:
          - key: example.io/example-key
            operator: In
            values:
            - example-value-1
            - example-value-2
      preferredDuringSchedulingIgnoredDuringExecution: <2>
      - weight: 1
        preference:
          matchExpressions:
          - key: example-node-label-key
            operator: In
            values:
            - example-node-label-value
...
----
<1> If you use the `requiredDuringSchedulingIgnoredDuringExecution` rule type, the VM is not scheduled if the constraint is not met.
<2> If you use the `preferredDuringSchedulingIgnoredDuringExecution` rule type, the VM is still scheduled if the constraint is not met, as long as all required constraints are met.