libvirt users - Apr 2012 - Is there a way for telling libvirt to auto define an xml under /etc/libvirt/qemu?

Hi everybody,
like in the subject: is there a way for telling libvirt to auto define
an xml under /etc/libvirt/qemu? I mean, sometimes it happens to have the
/etc/libvirt/qemu shared between nodes, say with a NFS share, since I
can set a new xml on a node and I want o see the virtual machine on all
the others, is there a way to automate this or am I obligated to launch
virsh define <xml> on EACH node?

Thank you so much,

-- 
Raoul Scarazzini
Solution Architect
MMUL: Niente ? impossibile da realizzare, se lo pensi bene!
+39 3281776712
rasca at mmul.it
http://www.mmul.it

On 26.04.2012 17:13, Raoul Scarazzini wrote:
> Hi everybody,
> like in the subject: is there a way for telling libvirt to auto define
> an xml under /etc/libvirt/qemu? I mean, sometimes it happens to have the
> /etc/libvirt/qemu shared between nodes, say with a NFS share, since I
> can set a new xml on a node and I want o see the virtual machine on all
> the others, is there a way to automate this or am I obligated to launch
> virsh define <xml> on EACH node?
> 
> Thank you so much,
> 
I'd say this is not supported as libvirt is not polling for changes on
XML files; That's what the warning at the beginning of each XML file
says. Therefore, if you change an XML from one host, the changes are
likely to get overwritten by libvirt on another host when shutting
libvirt down.

Michal

On 04/26/2012 09:13 AM, Raoul Scarazzini wrote:
> Hi everybody,
> like in the subject: is there a way for telling libvirt to auto define
> an xml under /etc/libvirt/qemu? I mean, sometimes it happens to have the
> /etc/libvirt/qemu shared between nodes,
*Don't do that. Ever.*

Each host _must_ have their own independent /etc/libvirt/qemu directory,
in order to allow proper migration between hosts.  There are only a few
directories specifically designed to be shared between hosts:

/var/lib/libvirt/images
/var/lib/libvirt/sanlock

and maybe a few others that are safe to share (because libvirt only
reads from, and never writes into them):

/etc/libvirt/hooks

Improperly sharing any other directories means that two libvirtd daemons
will stomp over each other, with potentially disastrous results on both
affected hosts involved in the conflicting usage.  For the same reason,
we recommend that you never directly edit files in /etc/libvirt, but
only use defined libvirt APIs to manage changes to your domains.
> say with a NFS share, since I
> can set a new xml on a node and I want o see the virtual machine on all
> the others, is there a way to automate this or am I obligated to launch
> virsh define <xml> on EACH node?
Yes, 'virsh define <xml>' on each node is the documented and
supported
way to maintain a persistent definition of the same domain across
multiple hosts.  Or you may want to look into VDSM (part of oVirt, and
available in Red Hat's RHEV product), which manages definitions of
domains across multiple hosts by using a common store managed by VDSM
and only using transient guests when using libvirt on any one host in
the managed cluster.

-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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