libvirt users - Dec 2013 - Re: Determine ongoing shutdown via libvirt or preventing migrations to host

Hi list,

Is there any function in libvirt to determine runlevel of host or any 
possibility to prevent VM migrations to that host ?

I'm developing simple cluster of 4 servers running KVM VMs. For 
management I decided to use python-libvirt. It is working in that way, 
that every VM is diskless and booting via PXE so I can run it on every 
host server. Every VM has assigned one host as monitor which is 
responsible to periodically check, that VM is running on one of other 
hosts. If it don't run, it will be started on first available server 
assigned for that VM. When one of hosts is shut down, it will migrate 
all VMs to another hosts, but that monitor which checks VMs will migrate 
it after reboot. But I have race condition there that monitors can check 
that host is running before it is shutdown and will migrate VM's back to 
server which will reboot.

Thank you for any help

--

Ondřej Kunc, Senior Linux Administrator

IGNUM s.r.o., Vinohradská 190, Praha 3, 130 61, CZE
Mobil: +420 603 111 111 | Fax: +420 296 332 222
www.ignum.cz | www.domena.cz | www.webcloud.cz

On Mon, Dec 09, 2013 at 01:01:43PM +0100, Ondřej Kunc
wrote:
> Hi list,
> 
> Is there any function in libvirt to determine runlevel of host or
> any possibility to prevent VM migrations to that host ?
> 
> I'm developing simple cluster of 4 servers running KVM VMs. For
> management I decided to use python-libvirt. It is working in that
> way, that every VM is diskless and booting via PXE so I can run it
> on every host server. Every VM has assigned one host as monitor
> which is responsible to periodically check, that VM is running on
> one of other hosts. If it don't run, it will be started on first
> available server assigned for that VM. When one of hosts is shut
> down, it will migrate all VMs to another hosts, but that monitor
> which checks VMs will migrate it after reboot. But I have race
> condition there that monitors can check that host is running before
> it is shutdown and will migrate VM's back to server which will
> reboot.
> 
> Thank you for any help
That kind of policy decision making is outside the scope of
libvirt I'm afraid. The higher level management tools using
libvirt would need to figure out that kind of stuff.


Daniel
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Hi Daniel,

Thank you for your reply. I agree that runlevel is not directly related 
to VM management so it is OK, that it is not implemented in libvirt 
library. What about prevention of VM migrations, is it acceptable to 
just close migration port in firewall ?

Thank you

Ondřej

Dne 10.12.2013 14:34, Daniel P. Berrange napsal(a):
> On Mon, Dec 09, 2013 at 01:01:43PM +0100, Ondřej Kunc wrote:
>> Hi list,
>>
>> Is there any function in libvirt to determine runlevel of host or
>> any possibility to prevent VM migrations to that host ?
>>
>> I'm developing simple cluster of 4 servers running KVM VMs. For
>> management I decided to use python-libvirt. It is working in that
>> way, that every VM is diskless and booting via PXE so I can run it
>> on every host server. Every VM has assigned one host as monitor
>> which is responsible to periodically check, that VM is running on
>> one of other hosts. If it don't run, it will be started on first
>> available server assigned for that VM. When one of hosts is shut
>> down, it will migrate all VMs to another hosts, but that monitor
>> which checks VMs will migrate it after reboot. But I have race
>> condition there that monitors can check that host is running before
>> it is shutdown and will migrate VM's back to server which will
>> reboot.
>>
>> Thank you for any help
>
> That kind of policy decision making is outside the scope of
> libvirt I'm afraid. The higher level management tools using
> libvirt would need to figure out that kind of stuff.
>
>
> Daniel
>

-- 
S pozdravem,

Ondřej Kunc, Senior Linux Administrator

IGNUM s.r.o., Vinohradská 190, Praha 3, 130 61, CZE
Mobil: +420 603 111 111 | Fax: +420 296 332 222
www.ignum.cz | www.domena.cz | www.webcloud.cz