monitoring

HCOMisconfiguredDescheduler

Meaning

A descheduler is a Kubernetes application that causes the control plane to re-arrange the workloads in a more optimized way.

The descheduler uses the Kubernetes eviction API to evict pods. However, KubeVirt VMs, which run as virt-launcher pods, require special handling so they can be properly migrated by KubeVirt through live migration.

In earlier releases, a specific profileCustomizations setting (devEnableEvictionsInBackground) was required to configure the descheduler correctly for KubeVirt. More recent releases include dedicated descheduler profiles that already handle this requirement.

Impact

Using the descheduler operator for KubeVirt VMs without the correct configuration may result in unstable or unpredictable behavior, which can negatively affect cluster stability.

Diagnosis

1. Check the KubeDescheduler custom resource (CR):

   kubectl get -n openshift-kube-descheduler-operator KubeDescheduler cluster -o yaml
   

2. Verify that the CR contains one of the following profile configurations:

   spec:
     profiles:
     - KubeVirtRelieveAndMigrate
   

   or

   spec:
     profiles:
     - DevKubeVirtRelieveAndMigrate
   

   or

   spec:
     profiles:
     - LongLifecycle
     profileCustomizations:
       devEnableEvictionsInBackground: true
   

If none of these are present, the Kube Descheduler Operator is not correctly configured for KubeVirt.

Mitigation

Configure the descheduler with an appropriate profile for your cluster. The order of preference is:

1. KubeVirtRelieveAndMigrate
2. DevKubeVirtRelieveAndMigrate
3. LongLifecycle with the devEnableEvictionsInBackground customization

To check which profiles are supported in your descheduler release, use the following command:

oc get crd kubedeschedulers.operator.openshift.io -o json | jq '.spec.versions[] | select(.name=="v1").schema.openAPIV3Schema.properties.spec.properties.profiles.items.enum[]'

Depending on the available profiles, apply one of the following configurations to the KubeDescheduler CR (kind: kubedeschedulers, namespace: openshift-kube-descheduler-operator, name: cluster):

• Configure the KubeVirtRelieveAndMigrate profile
  ```yaml spec: profiles:
  • KubeVirtRelieveAndMigrate ```
• Configure the DevKubeVirtRelieveAndMigrate profile
  ```yaml spec: profiles:
  • DevKubeVirtRelieveAndMigrate ```
• Configure the LongLifecycle profile with the devEnableEvictionsInBackground profile customization
  ```yaml spec: profiles:
  • LongLifecycle profileCustomizations: devEnableEvictionsInBackground: true ```
• If none of the listed steps are possible, remove the Kube Descheduler Operator.

If you cannot resolve the issue, see the following resources:

• OKD Help
• #virtualization Slack channel

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