Comment 1 for bug 1826888

TRIAGE:

So changing libvirt-image-backend for a nova host after creating instances is not a supported feature of the nova-compute charm, because (I suspect) it's not supported on nova itself. That doesn't mean that a new nova-compute (juju) application couldn't have a different libvirt-image-backend and co-exist with the other nova-compute (juju) application.

However, I agree that a documentation update would be useful to indicate that it shouldn't be done and work-arounds, and also in the config.yaml for the nova-compute charm.

It's possibly a good idea to actually make the config option and install time only config option (i.e. for it to have no effect if changed after the charm is installed). However, that might cause more problems that it solves.