The root issue here is the libvirt connection getting reset and then the libvirt driver code automatically setting the host to disabled so the scheduler skips over it and can't schedule the instance. So tracking this as a dupe of bug 1255624.
The root issue here is the libvirt connection getting reset and then the libvirt driver code automatically setting the host to disabled so the scheduler skips over it and can't schedule the instance. So tracking this as a dupe of bug 1255624.