[openstack-dev] [Nova][Neutron] nova-network in Icehouse and beyond

Vishvananda Ishaya vishvananda at gmail.com
Wed Jan 29 21:13:58 UTC 2014

On Jan 29, 2014, at 10:45 AM, Dan Smith <dms at danplanet.com> wrote:

>> I was thinking for the upgrade process that we could leverage the port
>> attach/detach BP done by Dan Smith a while ago. This has libvirt support
>> and there are patches pending approval for Xen and Vmware. Not sure about
>> the other drivers.
>> If the guest can deal with the fact that the nova port is being removed
>> and a new logical port is added then we may have the chance of no down
>> time. If this works then we may need to add support for nova-network port
>> detach and we may have a seamless upgrade path.
> That's a good thought for sure. However, it would be much better if we
> could avoid literally detaching the VIF from the guest and instead just
> swap where the other end is plugged into. With virtual infrastructure,
> that should be pretty easy to do, unless you're switching actual L2
> networks. If you're doing the latter, however, you might as well reboot
> the guest I think.
> —Dan

I did a very brief investigation into this about six months ago moving
nova-network over to l3-agent using ovs. I think it should be possible, but
I got a little bit stuck on a technical point and then got involved with
other things. I see the process as going something like this:

* Migrate network data from nova into neutron
* Turn off nova-network on the node
* Run the neutron l3 agent and trigger it to create the required bridges etc.
* Use ovsctl to remove the vnic from the nova bridge and add it to the appropriate ovs bridge

Because the ovs bridge and the nova bridge are plugged in to the same physical
device, traffic flows appropriately.

There is some hand waving above about how to trigger the l3 agent to create the
ports and security groups properly, but I think conceptually it could work.

I tried to do the above via devstack but it isn’t quite trivial to get devstack
to install and run neutron without deleting everything and starting over. Even
this doesn’t seem particularly hard, I just ran out of time to focus on it.

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