Warning: Longhorn will not start if Priority Class setting is invalid (such as the Priority Class not existing). You can see if this is the case by checking the status of the longhorn-manager DaemonSet with kubectl -n longhorn-system describe daemonset.apps/longhorn-manager. You will need to uninstall Longhorn and restart the installation if this is the case.
After Longhorn Installation
The Priority Class setting can be found in the Longhorn UI:
Setting -> General -> Priority Class
Users can update or remove the Priority Class here, but note that this will result in recreation of all the Longhorn system components. The Priority Class setting will reject values that appear to be invalid Priority Classes.
Before modifying the Priority Class setting, all Longhorn volumes must be detached.
Since all Longhorn components will be restarted, the Longhorn system will temporarily be unavailable. If there are running Longhorn volumes in the system, Longhorn system will not be able to restart its components, and the request will be rejected.
Don’t operate the Longhorn system after modifying the Priority Class setting, as the Longhorn components will be restarting.
Do not delete the Priority Class in use by Longhorn, as this can cause new Longhorn workloads to fail to come online.