I have an environment where I have the following on a metal:
ceph-osd
swift-storage
nova-compute
I started at xenial-pike and upgraded to xenial-queens on ceph-osd through the action-managed-upgrade process, however ran into no UCA archive change due to lp1778823.
I then moved on to swift-storage. I had to workaround a swift-storage bug lp#1817384 to "force" the upgrade.
When completed, I checked my juju model status and found nova-compute complaining about nova-compute service not running.
Connecting to the host, I get the log ERROR oslo_service.service RemoteError: Remote error: IncompatibleObjectVersion Version 1.4 of MigrationList is not supported in the nova-compute.log
nova-cloud-controller, neutron-api, etc are still running under pike versions, which is why they are crashing, as I'm still in group 2 of my upgrade per https://docs.openstack.org/project-deploy-guide/charm-deployment-guide/latest/app-upgrade-openstack.html#upgrade-order
This is forcing my hand into a very rushed upgrade since nova-compute is supposed to be group 4 upgraded.
I believe it's reasonable to expect that ceph-osd, nova-compute, and swift-storage could all be smooshed on the same metal and interactions of these three apps on the same unit doing openstack release upgrades would be very helpful.
Something I've noted, we've not run into this in the past as nova-compute has been in our personal "order of upgrade" to be upgraded before swift-storage.
Here's the classic Bootstack ordering we've used in the past. As you can see, nova-compute updating n-ovs and ceilometer-agent was well known in the past, so I believe nova-compute may have the same issue as just was witnessed with swift-storage when smooshed/co-located on the same metal.
Ceph-osd
Ceph-mon
ceph-radosgw
Keystone
Glance
Nova-
Neutron-api
Nova-compute
Neutron-
Neutron-gateway
Cinder
Swift-proxy
Swift-storage
Openstack-
Heat
Ceilometer
Gnocchi
Ceilometer-