Hi Gilles,
 
Regarding Xenial - Bionic upgrade - it's a possible upgrade, but it looks like more one-by-one re-setup than upgrade, if you wish to upgrade not only host OS, but containers as well. First of all you'll need to complete Q->R upgrade, after that you'll be able to upgrade Ubuntu.  For instance I've completed such upgrade for my deployments, and it was pretty successful. We've got some notes regarding such upgrade on etherpad: https://etherpad.openstack.org/p/osa-rocky-bionic-upgrade
 
Mixed deployments are supported by OSA as well - you may easily use different operating systems in one deployment, you just need wheels and packages to be build on the repo-server for this OS.
As far as I know work on upgrade Rocky->Stein is still in progress.
 
13.04.2019, 12:21, "Gilles Mocellin" <gilles.mocellin@nuagelibre.org>:
> Hello,
>
> I'm actually using OpenStack-Ansible to deploy a little public cloud. For now
> it runs on Queens / Ubuntu 16.04.
>
> I've read that Rocky will be the only release supported on both Ubuntu 16.04
> and Ubuntu 18.04 with OpenStack-Ansible.
> Stein being out soon (with OpenStack-Ansible), the question of Host OS upgrade
> from Ubuntu 16.04 to ubuntu 18.04 is a big thing of this year.
>
> I've not found any documentation about that upgrade path (Rocky->Stein, host
> OS).
> I had some answers on IRC that OpenStack Ansible does not support a mixed
> environnement (adding compute nodes on Ubuntu 18.04 while the rest is on
> Ubuntu 16.04 for example).
>
> Did I miss something in the actual doc or in some blogs ?
>
> I'm sure some users already faced this with transition fro Ubuntu 14.04 to
> Ubuntu 16.04. There's certainly some material to start some documentation and
> add it to https://docs.openstack.org/openstack-ansible/stein/admin/upgrades/
> major-upgrades.html.
>
> I know that there's less contributors now, I'll see if I can help.
>
> Thanks.
 
-- 
Kind Regards,
Dmitriy Rabotyagov