[Engine-devel] live migration and different technologies

[Itamar Heim]

On 06/08/2012 06:54 PM, Daniel P. Berrange wrote:
> On Wed, Jun 06, 2012 at 05:15:53PM +0300, Itamar Heim wrote:
>> Hi Daniel,
>>
>> on the quantum-ovirt call today the question of live migration
>> between multiple technologies was raised.
>>
>> iirc, you implemented the abstraction in libvirt between what the
>> guest sees and the actual host networking implementation for live
>> migration.
>>
>> can you please share if there are any considerations around live
>> migrations across different network implementations (bridge, sr-iov,
>> ovs, qbg, openflow, etc.)
>
> Yes, we added the ability to use libvirt's 'virtual network' APIs
> (virNetworkXXXXX) to define host networks using bridging, macvtap,
> etc, etc. A guest's NICs can then be configured solely using
> <interface type='network'>. This means that the guest XML will
> not have any host-specific data in it, as you see when using
> <interface type='bridge'>  or<interface type='direct'>
>
> This means you can migrate between machines where the bridges have
> different names (eg br0 on host A and br7 on host B), without any
> limitations.
>
> You can also migrate between different impls of the same technology
> (eg traditional software bridging vs macvtap bridging without
> limitations.
>
> Finally, you can migrate between completely different technologies
> (eg bridging vs vepa), but you will likely loose connectivity in
> the guests, since the technologies are not compatible at the ethernet
> layer.

can you please explain this point - how would packet going out of the 
host or arriving to the guest would be different between a bridged and a 
vepa implemtnaiton?

>
> In summary, libvirt configuration ability should not be the limiting
> factor in migrating between hosts with different networking config.
> You should only be limited by the ethernet/kernel level compatibility.
>
> Daniel