celery-graceful-stop

Celery plugin provides ability of graceful worker stopping.

Problem

Production deployment of long running tasks require worker to be stopped gracefully. Unfortunately celery got different behaviour:

1. Receiving SIGTERM signal by celery results starting Warm shutdown procedure. Due this procedure, inspect and control commands become unavailable.
2. More than that, all tasks are terminated forcely by the second SIGTERM with the Cold shutdown procedure.

This module provides more consistent approach to this problem, it

1. overrides SIGTERM receiver to prevent default Warm shutdown and Cold shutdown worker behaviour,
2. forces inspect and control commands to be working even after SIGTERM signal received.

Installation & Setup

pip install git+https://github.com/MnogoByte/celery-graceful-stop.git

Append your proj/celery.py file containg app instance with the following lines.

import celery_graceful_stop
celery_graceful_stop.register(app)

Settings

• CELERY_GRACEFUL_STOP (boolean). Controls graceful stop function. (True by default)

Using with systemd

1. Define 1 service per each worker you got (systemd require only one master pid for restart).
2. Provide /etc/conf.d/celery_<service_name> configuration file for each worker.
3. Add celery@.service file into your system.
4. Register your service with systemctl enable celery@<service_name>.

Limitations

• This module disables pool_shrink, pool_grow, autoscale, pool_reload, add_consumer, cancel_consumer control commands after receiving SIGTERM signal. Actually, you'll does not need to call them when the worker is shutting down, because worker will not starts new tasks.
• This module has been tested only with celery 3.1 with pool=prefork.

Author

Antonov Mikhail

License

BSD - 3