Comment 10 for bug 1845244

Got it! It's caused by a Docker issue, and our use of SIGHUP in ansible/roles/nova/tasks/refresh_scheduler_cell_cache.yml.

You can reproduce the issue as follows:

docker kill --signal HUP nova_scheduler
systemctl restart docker
docker ps -a | grep nova_scheduler

Docker assumes that the signal will stop the container, and marks it as not being restartable. However SIGHUP typically does not stop a process.

This is captured in Docker bug https://github.com/moby/moby/issues/11065. Their solution appears to be to use --stop-signal to define which signal should be used to stop the container. This does not appear to work in my testing however.