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…nfiguredDescheduler Add HCOMisconfiguredDescheduler runbook
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# HCOMisconfiguredDescheduler | ||
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## Meaning | ||
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A Descheduler is a Kubernetes application that causes the control plane to | ||
re-arrange the workloads in a better way. | ||
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The descheduler uses the Kubernetes eviction API to evict pods, and receives | ||
feedback from `kube-api` whether the eviction request was granted or not. | ||
On the other side, in order to keep VM live and trigger live-migration, | ||
KubeVirt handles eviction requests in a custom way and unfortunately | ||
a live migration takes time. | ||
So from the descheduler's point of view, `virt-launcher` pods fail to be | ||
evicted, but they actually migrating to another node in background. | ||
So the way KubeVirt handles eviction requests causes the descheduler to | ||
make wrong decisions and take wrong actions that could destabilize the cluster. | ||
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To correctly handle the special case of `VM` pod evicted triggering a live | ||
migration to another node, the `Kube Descheduler Operator` introduced | ||
a `profileCustomizations` named `devEnableEvictionsInBackground` | ||
which is currently considered an `alpha` feature | ||
on `Kube Descheduler Operator` side. | ||
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## Impact | ||
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Using the descheduler operator for KubeVirt VMs without the | ||
`devEnableEvictionsInBackground` profile customization can lead to | ||
unstable or oscillatory behavior, undermining cluster stability. | ||
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## Diagnosis | ||
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1. Check the CR for `Kube Descheduler Operator`: | ||
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```bash | ||
$ kubectl get -n openshift-kube-descheduler-operator KubeDescheduler cluster -o yaml | ||
``` | ||
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looking for: | ||
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```yaml | ||
spec: | ||
profileCustomizations: | ||
devEnableEvictionsInBackground: true | ||
``` | ||
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If not there, the `Kube Descheduler Operator` is not correctly configured | ||
to work alongside KubeVirt. | ||
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## Mitigation | ||
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Set: | ||
```yaml | ||
spec: | ||
profileCustomizations: | ||
devEnableEvictionsInBackground: true | ||
``` | ||
on the CR for the `Kube Descheduler Operator` or | ||
remove the `Kube Descheduler Operator`. | ||
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Please notice that `EvictionsInBackground` is an alpha feature, | ||
and it's subject to change and currently provided as an | ||
experimental feature. | ||
<!--DS: If you cannot resolve the issue, log in to the | ||
link:https://access.redhat.com[Customer Portal] and open a support case, | ||
attaching the artifacts gathered during the diagnosis procedure.--> | ||
<!--USstart--> | ||
If you cannot resolve the issue, see the following resources: | ||
- [OKD Help](https://okd.io/docs/community/help) | ||
- [#virtualization Slack channel](https://kubernetes.slack.com/channels/virtualization) | ||
<!--USend--> |
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