[libvirt-users] live migration and config

[Jiri Denemark]

On Fri, Sep 14, 2018 at 16:00:43 +0400, Dmitry Melekhov wrote:
> 14.09.2018 15:43, Jiri Denemark пишет:
> > On Thu, Sep 13, 2018 at 19:37:00 +0400, Dmitry Melekhov wrote:
> >>
> >> 13.09.2018 18:57, Jiri Denemark пишет:
> >>> On Thu, Sep 13, 2018 at 18:38:57 +0400, Dmitry Melekhov wrote:
> >>>> 13.09.2018 17:47, Jiri Denemark пишет:
> >>>>> On Thu, Sep 13, 2018 at 10:35:09 +0400, Dmitry Melekhov wrote:
> >>>>>> After some mistakes yesterday we ( me and my colleague ) think that it
> >>>>>> will be wise for libvirt to check config file existence on remote side
> >>>>> Which config file?
> >>>>>
> >>>> VM config file, namely qemu.
> >>> Do you mean the domain XML definition found in /etc/libvirt/qemu/*.xml ?
> >> Yes and no, xml, but at another location.
> >>
> >>>> We forgot to mount shared storage (namely gluster volume), on which we
> >>>> have config files, twice...
> >>> If you're talking about the domain XML file, then you should never store
> >>> them on a shared storage. All XML files in /etc/libvirt are supposed to
> >>> be local to each host.
> >> They are not stored in /etc/libvirt , but in other location, which is
> >> suitable for sharing.
> > I'm even more confused now. How could libvirt even know about such
> > files? Unless you use transient domains, i.e., point libvirt to the
> > right XML when starting the domain.
> 
> Yes, it transient, really, we use pacemaker's VirtualDomain
> http://www.linux-ha.org/wiki/VirtualDomain_(resource_agent)
> 
> pacemaker creates domain and destroys it.
> 
> As I can see from sources migration looks like:
> virsh ${VIRSH_OPTIONS} migrate --live $migrate_opts $DOMAIN_NAME 
> $remoteuri $migrateuri &
> 
> Don't know which exact options it uses though.
> 
> Do we need xml on another host if domain is transient for live migration?

No, the XML is only needed when starting the domain. At the beginning of
migration libvirt transfers the XML to libvirtd on the other host so
that QEMU with the right parameters can be started there.

Just to make sure, the disk images used by the domain are stored on a
shared storage accessible from both hosts, right?

Jirka