[ovirt-users] Manually starting VMs via vdsClient (HE offline)

[Dan Yasny]

On Wed, Feb 8, 2017 at 4:18 PM, Doug Ingham <dougti at gmail.com> wrote:

> Hi Dan,
>
> On 8 February 2017 at 18:10, Dan Yasny <dyasny at gmail.com> wrote:
>
>>
>>
>> On Wed, Feb 8, 2017 at 4:07 PM, Doug Ingham <dougti at gmail.com> wrote:
>>
>>> Hi Guys,
>>>  My Hosted-Engine has failed & it looks like the easiest solution will
>>> be to install a new one. Now before I try to re-add the old hosts (still
>>> running the guest VMs) & import the storage domain into the new engine, in
>>> case things don't go to plan, I want to make sure I'm able to bring up the
>>> guests on the hosts manually.
>>>
>>> The problem is vdsClient is giving me an "Unexpected exception", without
>>> much more info as to why it's failing.
>>>
>>> Any idea?
>>>
>>> [root at v0 ~]# vdsClient -s 0 list table | grep georep
>>> 9d1c3fef-498e-4c20-b124-01364d4d45a8  30455  georep-proxy         Down
>>>
>>> [root at v0 ~]# vdsClient -s 0 continue 9d1c3fef-498e-4c20-b124-01364d
>>> 4d45a8
>>> Unexpected exception
>>>
>>> /var/log/vdsm/vdsm.log
>>> periodic/1063::WARNING::2017-02-08 17:57:52,532::periodic::276::v
>>> irt.periodic.VmDispatcher::(__call__) could not run <class
>>> 'vdsm.virt.periodic.DriveWatermarkMonitor'> on
>>> ['65c9807c-7216-40b3-927c-5fd93bbd42ba', u'9d1c3fef-498e-4c20-b124-0136
>>> 4d4d45a8']
>>>
>>>
>> continue meane un-pause, not "start from a stopped state"
>>
>
> I search the manual for start/init/resume syntax, and "continue" was the
> closest thing I found.
>

I don't have a 4.x vdsm handy, but on 3.6 the verb is "create". With a LOT
of params of course.


>
>
>> now having said that, if you expect the VMs not to be able to start after
>> you rebuild the engine and the VMs exist on the hosts, I'd collect a virsh
>> -r dumpxml VMNAME for each - that way you have the disks in use, and all
>> the VM configuration in a file, and with some minor LVM manipulation you'll
>> be able to start the VM via virsh
>>
>
> My main concern is that I might have to halt the VMs or VDSM services for
> some reason when trying to migrate to the new engine. I just want to make
> sure that no matter what happens, I can still get the VMs back online.
>

The way oVirt works is very much tied into the engine DB. When you click
"start" on a VM, the engine will query the DB, pull out the VM details (CPU
config, disks, RAM etc), pick a suitable host, enable the hosts' access to
the disks on the storage domain, generate the libvirt domxml for the VM
(the file you'd get from virsh dumpxml) and start the VM according to the
generated XML. With vdsClient and without the engine DB you'll be missing
all those details the database provides, while my way, with the XML, they
are all already in place, populated by the engine when it was still alive.


>
> I'm still getting myself acquainted with virsh/vdsClient. Could you
> provide any insight into what I'd have to do to restart the guests manually?
>
>
see above. But seriously, above all, I'd recommend you backup the engine
(it comes with a utility) often and well. I do it via cron every hour in
production, keeping a rotation of hourly and daily backups, just in case.
It doesn't take much space or resources, but it's more than just best
practice - that database is the summary of the entire setup.



> Thanks,
> --
> Doug
>
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