We use Celery with our Django webapp to manage offline tasks; some of these tasks can run up to 120 seconds.
Whenever we make any code modifications, we need to restart Celery to have it reload the new Python code. Our current solution is to send a SIGTERM to the main Celery process (kill -s 15 `cat /var/run/celeryd.pid`
), then to wait for it to die and restart it (python manage.py celeryd --pidfile=/var/run/celeryd.pid [...]
).
Because of the long-running tasks, this usually means the shutdown will take a minute or two, during which no new tasks are processed, causing a noticeable delay to users currently on the site. I'm looking for a way to tell Celery to shutdown, but then immediately launch a new Celery instance to start running new tasks.
Things that didn't work:
ERROR: Pidfile (/var/run/celeryd.pid) already exists. Seems we're already running? (PID: 13214)
and dies immediately. (This looks like a bug in Celery itself; I've let them know about it.)celeryd has --autoreload option. If enabled, celery worker (main process) will detect changes in celery modules and restart all worker processes. In contrast to SIGHUP signal, autoreload restarts each process independently when the current executing task finishes. It means while one worker process is restarting the remaining processes can execute tasks.
http://celery.readthedocs.org/en/latest/userguide/workers.html#autoreloading