Comment 1 for bug 2016157

I'm wondering if this is a python2 -> python3 issue; i.e. at queens it is python2, but at rocky the payload is python3. So the cinder charm purges the python2 packages (as indicated in the bug report), but this obviously clobbers nova/neutron due to the common packages.

It's quite a tricky problem as the common packages are needed, but that means that you can't have rocky cinder + queens nova-compute on the same host.

I wonder if nova-compute has been upgraded to rocky as well, that it would have re-installed the packages?

In terms of fixing this issue, we'd probably have to alter the cinder charm code to leave behind the shared packages if it's configured as a volume charm, rather than nuke everything on upgrade.