Comment 9 for bug 1328546

The race condition still exists.

Neutron happens to delete the bridge [1] between plug_vifs (ensure_bridge) [2] and _create_domain [3] if your instance is the only one using the bridge.

I locally fix it by disabling remove_empty_bridges and using a cron to delete empty bridges instead.

[1] https://github.com/openstack/neutron/blob/6cf92011143eb55adda180ffac91886566fc7826/neutron/plugins/linuxbridge/agent/linuxbridge_neutron_agent.py#L926
[2] https://github.com/openstack/nova/blob/f9e664f1b6521dd7d5c02cd803e376e8abdf9c30/nova/virt/libvirt/driver.py#L4383
[3] https://github.com/openstack/nova/blob/f9e664f1b6521dd7d5c02cd803e376e8abdf9c30/nova/virt/libvirt/driver.py#L4390