On Fri, Jun 14, 2019 at 3:02 PM Strahil <hunter86_bg(a)yahoo.com> wrote:
On Jun 13, 2019 16:14, Gianluca Cecchi <gianluca.cecchi(a)gmail.com> wrote:
>
> Hello,
> I would like to know in better detail how soft fencing works in 4.3.
> In particular, with "soft fencing" we "only" mean vdsmd restart
attempt,
correct?
Yes, it just restarts vdsmd service using SSH connection. In the past we
had several cases, where VDSM was non-responsive, but VMs were running
fine, that's why we added this as the 1st step in non-responding treatment
flow.
We try to connect to host using SSH, restarts VDSM and waits if host start
communicate again. If there is an error during SSH connection or service
restart, we immediately continue to next phase of the treatment.
Who is responsible for issuing the command? Manager or host itself?
The manager should take the decision, but the actual command should be
done by another host.
The manager, this flow is started from host monitoring if there a network
error or connection timeout ...
> Because in case of Manager, if the host has already lost
connection, how
could the manager be able to do it?
Soft fencing is ussed when ssh is available. In all other cases it doesn't
work.
So if engine cannot communicate with host, we don't know the reason, so
there are several steps in non-responding treatment:
1. SSH Soft Fencing
2. Kdump detection (if it's configured for the host and we detecte host is
dumping, we can restart HA VMs on different host)
3. Power Management restart
- according to cluster fencing policy we can skip restarting host if
for exampl host is renewing its storage lease or gluster cluster is healing
- this part is executed on different host in the same cluster/data
center
If you want to know more about fencing in oVirt, please take a look at
below links:
Host fencing in oVirt - Fixing the unknown and allowing VMs to be highly
available
https://www.youtube.com/watch?v=V1JQtmdleaM
Integrating kdump into oVirt
https://www.youtube.com/watch?v=RAGV_za_Qvw
Automatic fencing in oVirt
https://www.ovirt.org/develop/developer-guide/engine/automatic-fencing.html
Fence-kdump integration in oVirt
https://www.ovirt.org/develop/release-management/features/infra/fence-kdu...
And course feel free to ask questions
Martin
Thanks in advance for clarifications and eventually documentation
pointers
oVirt DOCs need a lot of updates, but I never found a way to add or edit a
page.
Best Regards,
Strahil Nikolov
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--
Martin Perina
Manager, Software Engineering
Red Hat Czech s.r.o.