Comment 4 for bug 1809061

Yeah, judging from the code line in the backtrace:

  2018-12-10 15:05:15.029 26837 ERROR oslo_messaging.rpc.server return (self.host_state_map[host] for host in seen_nodes)

they're running a version earlier than Queens or had pulled Queens from master before fixes landed.

This bug looks like a duplicate of:

  https://bugs.launchpad.net/nova/+bug/1739323

which was fixed by this change:

  https://review.openstack.org/529352

which was backported to Pike and Ocata at the time.