[ovirt-users] Two ovirt-engine manage one hypervisor

[Yedidyah Bar David]

On Thu, Jun 16, 2016 at 10:13 AM, Michal Skrivanek
<michal.skrivanek at redhat.com> wrote:
>
> On 16 Jun 2016, at 09:07, Yaniv Kaul <ykaul at redhat.com> wrote:
>
>
>
> On Thu, Jun 16, 2016 at 9:29 AM, Yedidyah Bar David <didi at redhat.com> wrote:
>>
>> On Thu, Jun 16, 2016 at 9:10 AM, Yaniv Kaul <ykaul at redhat.com> wrote:
>> >
>> >
>> > On Thu, Jun 16, 2016 at 8:53 AM, Yedidyah Bar David <didi at redhat.com>
>> > wrote:
>> >>
>> >> On Thu, Jun 16, 2016 at 5:33 AM, Sandvik Agustin
>> >> <agustinsandvik at gmail.com> wrote:
>> >> > Hi users,
>> >> >
>> >> > Good day, is it possible to configure two ovirt-engine to manage one
>> >> > hypervisor? My purpose for this is what if the first ovirt-engine
>> >> > fails,
>> >> > I
>> >> > still have the 2nd ovirt-engine to manage hypervisor.
>> >> >
>> >> > is this possible? or any suggestion similar to my purpose?
>> >>
>> >> The "normal" solution is hosted-engine, which has HA - the engine
>> >> runs in a VM, and HA daemons monitor it and the hosts, and if there
>> >> is a problem they can start it on another host.
>> >>
>> >> There were discussions in the past, which you can find in the list
>> >> archives,
>> >> about running two engines against a single database, and current bottom
>> >> line
>> >> is that it's not supported, will not work, and iiuc will require some
>> >> significant development investment to support.
>> >>
>> >> You might manage to have an active/passive solution - install an engine
>> >> on two machines, configure both to use the same remote database, but
>> >> make sure only one of them is active at any given time. Not sure if
>> >> that's
>> >> considered "fully supported", but might come close.
>
>
> even when you make it work when cert issues are sorted out, you need to be
> very careful not to bring both engines up managing a same host, they will
> fight over it and the monitoring is going to be received only by one of the
> engines, which in turn may cause HA VMs restart and split brains all over
> the place.

And, IIRC from previous discussions, also internal caches etc.

But this is not something specific to ovirt-engine - many services
have similar restrictions, and common clustering tools allow handling
them.

>
>> >
>> >
>> > That's not enough - they need to share the same set of certificates...
>>
>> Best is to simply clone the machine after initial setup then change
>> what's needed, or backup/restore only files (engine-backup --mode=backup
>> --scope=files).
>>
>> Didn't check, but I do not think they actually need all the certs of
>> all hosts - that is, that it's not mandatory to keep /etc/pki synced
>> between them after initial setup. Didn't try that myself.
>
>
> I'm not sure what happens when you provision a host from Mgmt A, then move
> to Mgmt B and provision another from it:
> 1. Mgmt A won't be aware of that host, from cert req perspective. May not be
> such a big deal - donno.
>
> 2. Can Mgmt A provision another host? Need to ensure the certificate serial
> numbers are OK, etc.
>
> They really need to share the CA DB.

Even keeping /etc/pki synced, or mounted from each one before
starting the engine and umounting when stopping, should not be
too hard.

> The backup-restore sounds like good approach  to me.
> Y.
>
>>
>> > Y.
>> >
>> >>
>> >>
>> >> You can find on the net docs/resources about creating a redundant
>> >> postgresql cluster.
>> >>
>> >> Best,
>> >> --
>> >> Didi
>> >> _______________________________________________
>> >> Users mailing list
>> >> Users at ovirt.org
>> >> http://lists.ovirt.org/mailman/listinfo/users
>> >
>> >
>>
>>
>>
>> --
>> Didi
>
>
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-- 
Didi