[one-users] Trying to understand the difference between OpenNebula vs. Libvirt

[Ruben S. Montero]

Hi

> So what does OpenNebula provide that libvirt doesn't? My take:

I think that is not the right angle to understand the role of each
component. OpenNebula and libvirt are totally different things, just
in the same way that Xen and libvirt are different. In fact there are
libvirt drivers for OpenNebula, as there are drivers for Xen.

You can interface your OpenNebula-based cloud with 5 interfaces:

* Native XML-RPC (with high-level bindings in Ruby, Java will be
released shortly)
* libvirt, check http://www.libvirt.org/drvone.html
* EC2 Query API
* OCCI
* RedHat's Delta Cloud, check http://www.deltacloud.org/drivers.html

So when using libvirt the relationship between OpenNebula & libvirt is:

* libvirt on-top-of OpenNebula: It provides you a widely adopted
interface to manage you cloud. So for example you can use virsh create
instead of onevm create.

* libvirt under OpenNebula: OpenNebula uses libvirt to interface KVM
in the cluster nodes.

You could have something like this to create a VM:

(virsh create) ---libvirt---> (OpenNebula - distributed management)
---libvirt---> KVM

So as Jack pointed out OpenNebula gives you the distributed management
(scheduler, image movement, networks...) and libvirt gives you an
interface to access that functionality.

Cheers

Ruben

On Wed, Feb 24, 2010 at 4:14 PM, Willem van Engen <wvengen at nikhef.nl> wrote:
> Hi,
>
> This is something I've asked myself as well.
> (comments below)
>
> Jack Jill wrote:
>>
>> On Tue, Feb 16, 2010 at 8:36 AM, Chintana Wilamuna <chintanaw at gmail.com
>> <mailto:chintanaw at gmail.com>> wrote:
>>
>>    Hi,
>>
>>    I'm trying to understand the difference between OpenNebula and
>>    Libvirt.
>>  OpenNebula is considered an IaaS solution than just a VM manager. It
>> orchestrates image storage (NFS, SCP, etc.). It handles setting up VMs with
>> a virtual network environment (VLANs). It interfaces with the hypervisor to
>> create and control VMs. OpenNebula comes with a default scheduler for
>> handling placement of VMs on hosts.
>> It also supports contextualization in VMs such as setting up IP address,
>> ssh keys, etc.
>
> The libvirt homepage www.libvirt.org mentions that it provides management of
> virtual machines, virtual networks and storage; so there is a little more
> overlap in functionality.
>
> The documentation of libvirt notes (Goals): "libvirt is intended to be a
> building block for higher level management tools and for applications
> focusing on virtualization of a single node (the only exception being domain
> migration between node capabilities which involves more than one node).".
> So I guess one could say that everything concerning a single node (physical
> machine) is covered by libvirt, and as such it would be comparable to
> OpenNebula's mads. (though I have seen no contextualisation in libvirt.)
>
>>    Trying to build a tool on top of OpenNebula which will be
>>    management interface. I'm really reluctant to use the XMLRPC
>>    interface. That leaves me with using the libvirt driver for
>>    OpenNebula. If I am to use that, as with my understanding OpenNebula
>>    becomes redundant isn't it. Why not skip OpenNebula altogether and use
>>    libvirt instead?
>>
>>  You could use LibVirt directly, but then you would be missing out on the
>> information captured by OpenNebula information agents in the SQLite database
>> that you would perhaps want to display on the management interface.
>
> So what does OpenNebula provide that libvirt doesn't? My take:
> * Awareness of multiple physical nodes
> * Contextualisation
> * Allocation of IP and MAC addresses
> Is this right?
>
> Regards,
> - Willem
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>



-- 
Dr. Ruben Santiago Montero
Associate Professor, Complutense University of Madrid

URL:    http://dsa-research.org/doku.php?id=people:ruben
Weblog: http://blog.dsa-research.org/?author=7