Comment 7 for bug 1682423

I hit the same thing when I upgraded to Ocata. I meant to update this issue after resolving, but out of mind...

I believe the issue was that not all of the compute nodes were successfully upgraded, so the messages are limited to an older version, and one of these failed. In my case, I went from Newton to Ocata, and upgraded all of the *active* compute nodes, but it turned out there were other *inactive* compute nodes still registered in the database, and these prevented the API from deciding that it was safe to use the newer messaging version.

I think there is a bug here, but I got past it by deleted the stale records from the database and restarting Nova. This allowed it to detect the latest version for all of the compute nodes, and switch to the Ocata messaging version.