Deleted KVM host is automatically re-added to the cluster after reboot

[Eddi1306]

problem

We removed a host from a CloudStack cluster containing multiple KVM hosts. Before deletion, the host was placed into maintenance mode, as required by CloudStack in order to remove it safely.

After the host had been deleted from CloudStack, the underlying physical server was rebooted because updates had been applied. The reboot itself was not expected to have any effect on CloudStack, since the host had already been removed from the management plane.

Unexpectedly, after the reboot, CloudStack rediscovered the machine and added it back to the same cluster as a new host. We also verified in the CloudStack database that the host entry had first been deleted and then recreated as a new record.

This behavior suggests that CloudStack is still able to rediscover a previously removed KVM host when the machine comes back online, even though it had already been deleted from CloudStack.

Expected behavior:

Once a host has been removed from CloudStack, rebooting the underlying physical server should not cause the host to be automatically rediscovered and re-added to the same cluster.

Actual behavior:

The deleted host was automatically added back to the cluster as a new host after the physical server reboot.

Environment:

CloudStack: 4.22.1.0

Hypervisor: KVM

Cluster: multiple hosts

Host state before deletion: maintenance mode

Host status after deletion: removed from CloudStack

Database observation: host entry was deleted and later recreated as a new entry

Additional details:

We did not manually re-add the host after deletion.

The host appears to have been rediscovered automatically by CloudStack after the reboot.

The issue occurred in a multi-host cluster environment.

versions

CloudStack version: 4.22.1.0

OS and database versions:
We observed this behavior in two CloudStack installations:

Management Server OS: Ubuntu 24.04 LTS

Database: MySQL 8.x

KVM Host OS: AlmaLinux 9.8 and Ubuntu 24.04 LTS

The steps to reproduce the bug

1. Migrate all VMs off the host.

2. Put the host into maintenance mode.

3. Remove the host from the cluster in CloudStack.

4. Reboot the physical server.

What to do about it?

No response

[boring-cyborg]

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[DaanHoogland]

@wido , you guys use the autodiscovery of hosts right? Can you comment?

@Eddi1306 , I think you need to make sure your remove the agent from the host to prevent the re-adding it?

[sbrueseke]

@DaanHoogland yes, you are correct, but I would expect that after deleting a host in ACS the host would not be able to rejoin automatically only by reboot. In the DB the original host will have state removed and after a simple reboot a new host with a new id will be added to the DB.
So maybe a better workflow is that when you delete a host the agent config will also be deleted from the host.