[PVE-User] Migration from server down

[Fabian Grünbichler]

On Thu, May 04, 2017 at 09:15:03AM +0200, Alessandro Briosi wrote:
> Hi all,
> I have had some troubles with 1 server in a cluster.
> As the VM have all disks on shared storage I though it would have been
> possible to migrate them from the current out of order server to the
> others in the cluster.
> HA is not enabled (I prefer doing it manual)
> 
> Though the GUI gave errors 'cause it could not connect to the server.
> 
> So I migrated it simply by moving the VM configuration to another node.
> 
> Am I missing something in the GUI? Why is it not possible to migrate a
> server (with all shared resources) to another server from the GUI when
> the VM is on a not reachable server?
> 
> IMHO there should be a path to change (and migrate) a VM configuration
> even if the server where it rus is down/not reachable.

because without HA/fencing you have no guarantee that the other node
is actually off, and not just not reachable. the same applies for any
guests potentially running there. "stealing" the guest (configuration)
is therefor potentially dangerous, and needs to be done manually. but
yes, it is just as simple as verifying that the guest is actually not
running on the other node (e.g., because the node is known to be
physically off) and that it has no local dependencies (storage or
otherwise) and then moving the file in /etc/pve.

if there were a button for this on the GUI, people would use it without
understanding the consequences, and then blame the tool instead of the
user when something goes wrong ;)

with HA, the HA stack takes care of this using
- proper locking
- fencing of non-quorate nodes

this ensures that when the HA stack steals a config after the
appropriate timeouts/.. have happened, there cannot be a
conflict/inconsistency.