libvirt users - Sep 2015 - Re: about guest live migration configuration changes persistence ..

Hi,

Thanks for infos.

My concern is the following :

In order to establish datas exchanges between hosts and guest , I'll add a
channel device to a running Guest ( as I learned from you  that it's 
possible to do that without stopping the Guest).
When the guest migrates to another host , this one must be able to retrieve the
channel device parameters to be able to dialog with the migrated guest.
I plan to use dumpxml to retrieve these  infos.
Will these infos be updated on the second host where  the guest has migrated ?

Thx.

J.P.

-----Message d'origine-----
De : Michal Privoznik [mailto:mprivozn@redhat.com] 
Envoyé : mercredi 2 septembre 2015 14:12
À : Jean-Pierre Ribeauville; libvirt-users@redhat.com
Objet : Re: [libvirt-users] about guest live migration configuration changes
persistence ..

On 31.08.2015 09:27, Jean-Pierre Ribeauville wrote:
> Hi,
> 
> 
> Is a change , by edit it via virsh edit  , in the "local" .xml 
> configuration file (i.e. adding a channel device)  persistent when live
migrating the guest on another host ?
Yes. Since the 0.9.7 release, the configuration XML is transferred to the other
side too. However, by default, migrated domains are just transient (unless you
pass VIR_MIGRATE_PERSIST_DEST flag, or virsh migrate --persistent ..) so the
configuration XML doesn't have much effect in that case.

Michal

On 03.09.2015 11:18, Jean-Pierre Ribeauville wrote:
> Hi,
> 
> Thanks for infos.
> 
> My concern is the following :
> 
> In order to establish datas exchanges between hosts and guest , I'll
add a channel device to a running Guest ( as I learned from you  that it's 
possible to do that without stopping the Guest).
> When the guest migrates to another host , this one must be able to retrieve
the channel device parameters to be able to dialog with the migrated guest.
> I plan to use dumpxml to retrieve these  infos.
> Will these infos be updated on the second host where  the guest has
migrated ?
Sure. Otherwise migration would be broken in general. I mean, if guest
uses say tap0 on the source, the device may already have been taken on
the destination. Libvirt must then find/create another free device for
the migrated domain to use, e.g. tap1. It's the same with other devices.
Even consoles. But if you're using channel device (assuming you're using
a unix socket as backend (=part visible within the host)), the path to
the socket should be preserved.

Michal

Hi,

Effectively, I use  unix socket as backend.

Thx for help.

J.P.
-----Message d'origine-----
De : Michal Privoznik [mailto:mprivozn@redhat.com] 
Envoyé : jeudi 3 septembre 2015 11:33
À : Jean-Pierre Ribeauville; libvirt-users@redhat.com
Objet : Re: [libvirt-users] about guest live migration configuration changes
persistence ..

On 03.09.2015 11:18, Jean-Pierre Ribeauville wrote:
> Hi,
> 
> Thanks for infos.
> 
> My concern is the following :
> 
> In order to establish datas exchanges between hosts and guest , I'll
add a channel device to a running Guest ( as I learned from you  that it's 
possible to do that without stopping the Guest).
> When the guest migrates to another host , this one must be able to retrieve
the channel device parameters to be able to dialog with the migrated guest.
> I plan to use dumpxml to retrieve these  infos.
> Will these infos be updated on the second host where  the guest has
migrated ?
Sure. Otherwise migration would be broken in general. I mean, if guest uses say
tap0 on the source, the device may already have been taken on the destination.
Libvirt must then find/create another free device for the migrated domain to
use, e.g. tap1. It's the same with other devices.
Even consoles. But if you're using channel device (assuming you're using
a unix socket as backend (=part visible within the host)), the path to the
socket should be preserved.

Michal