[libvirt-users] live migration and config

[Dmitry Melekhov]

14.09.2018 16:15, Jiri Denemark пишет:
> 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.
Well, then it is really strange...
> Just to make sure, the disk images used by the domain are stored on a
> shared storage accessible from both hosts, right?
>
Yes, we use gluster and connection over gfapi, so VM storage is 
accessible from all hosts.
Usually, when xml are available, migration works without problems.

Just thought - it is possible that problem is in pacemaker's 
VirtualDomain and it needs xml on all hosts,
there is such comment :

# During a probe, it is permissible for the config file to not be
# readable (it might be on shared storage not available during the
# probe). In that case, we're
# unable to get the domain name. Thus, we also can't check whether the
# domain is running. The only thing we can do here is to assume that
# it is not running.


We have to check, but looks like we have to ask in pacemaker mail list, 
it has to check if xml is available.

Thank you!