A descheduler is a Kubernetes application that causes the control plane to re-arrange the workloads in a better way.
The descheduler uses the Kubernetes eviction API to evict pods, and receives
feedback from kube-api on whether the eviction request was granted.
In contrast, to keep a VM live and trigger a live migration,
KubeVirt handles eviction requests in a custom manner,
and a live migration takes time to perform.
Therefore, when a virt-launcher pod is migrating to another node in the background,
the descheduler detects this as a pod that failed to be evicted. As a consequence,
the manner in which KubeVirt handles eviction requests causes the descheduler
to make incorrect decisions and take incorrect actions that might destabilize the cluster.
To correctly handle the special case of an evicted VM pod triggering a live
migration to another node, the Kube Descheduler Operator introduced
a profileCustomizations named devEnableEvictionsInBackground.
This is currently considered an alpha feature for
on Kube Descheduler Operator.
Using the descheduler operator for KubeVirt VMs without the
devEnableEvictionsInBackground profile customization might lead
to unstable or unpredictable behavior, which negatively impacts cluster stability.
Check the CR for Kube Descheduler Operator:
$ kubectl get -n openshift-kube-descheduler-operator KubeDescheduler cluster -o yaml
Search for the following lines in the CR:
spec:
profileCustomizations:
devEnableEvictionsInBackground: true
If these lines are not present, the Kube Descheduler Operator is not correctly configured
to work alongside KubeVirt.
Do one of the following:
Kube Descheduler Operator:
spec:
profileCustomizations:
devEnableEvictionsInBackground: true
Kube Descheduler Operator.Note that EvictionsInBackground is an alpha feature,
and as such, it is provided as an experimental feature
and is subject to change.
If you cannot resolve the issue, see the following resources: