Hi Christian, I documented this a few months ago here: https://www.jimmdenton.com/migrating-lxb-to-ovn/. It’s heavily geared towards OpenStack-Ansible, but you can probably extrapolate the steps for a vanilla deployment or other deployment tool. The details will vary. Highly recommend testing this in a lab environment that mirrors production, if possible. -- James Denton Principal Architect Rackspace Private Cloud - OpenStack james.denton@rackspace.com From: Christian Rohmann <christian.rohmann@inovex.de> Date: Wednesday, November 23, 2022 at 4:27 AM To: James Denton <james.denton@rackspace.com>, Slawek Kaplonski <skaplons@redhat.com>, openstack-discuss@lists.openstack.org <openstack-discuss@lists.openstack.org> Subject: Re: [neutron] Switching the ML2 driver in-place from linuxbridge to OVN for an existing Cloud CAUTION: This message originated externally, please use caution when clicking on links or opening attachments! Hey James, I am really sorry I just get back to you now. On 29/08/2022 19:54, James Denton wrote: In my experience, it is possible to perform in-place migration from ML2/LXB -> ML2/OVN, albeit with a shutdown or hard reboot of the instance(s) to complete the VIF plugging and some other needed operations. I have a very rough outline of required steps if you’re interested, but they’re geared towards an openstack-ansible based deployment. I’ll try to put a writeup together in the next week or two demonstrating the process in a multi-node environment; the only one I have done recently was an all-in-one. James Denton Rackspace Private Cloud Thanks for replying, I'd really love to see your outline / list of steps. BTW, we are actively working on switching to openstack-ansible - so that would suit us well. We also came to the conclusion that a shutdown of all instances might be required. Question is, if that has to happen instantly or if one could do that on a project by project base. Our cloud is small enough to still make this feasible, but I suppose this topic is or will become more important to other, larger clouds as well. Regards Christian