Comment 12 for bug 921294

My main concerns come from looking at this from a packagers perspective. With things like XCP support in Ubuntu coming closer to seeing the light of day, this kinda stuff makes it really difficult to have a nova-common package that can work out of the box with any corresponding compute setup/package. Granted, currently only libvirt is really supported and we already make assumptions about this in the common nova.conf. Working around this by adding '--connection_type=' to nova.conf in nova-common is doable in the short term, but if we want packaging to support a variety of configurations (I do), we might (packagers) need to rethink some things (perhaps nova-common-{libvirt, xcp, etc})

Do I understand the proposed solution?

- New users with empty databases and no connection_type get the xen version by default.
- Exsitng users with data in the database will need to specify connection_type explicitly during migration
- From Ubuntu POV, we can continue to be opinionated about what users are deploying, and set connection_type explicitly=libvirt in packaging