Comment 4 for bug 2072311

My comment from: https://github.com/canonical/charmed-openstack-upgrader/issues/466#issuecomment-2230931757

The general approach would be, for a single machine.

a) Make sure all the charms are up to date for their channel first. `juju refresh`
b) Make sure that openstack-origin/source is pointing to the current version (i.e. is not the 'default' unset state).
c) Switch charms to the next channel (subordinates and principles) - `juju switch`
d) Switch the openstack-origin/source of the principle charms `juju config` (and perhaps `juju run ... openstack-upgrade`.

This would ensure the best chance of success. I think with this approach, any errors are then a bug that should be fixed.