Celery- signal to detect idle workers

Question

I 1 celery broker and several celery workers, all communicating with rabbitMQ. In my setup, I send several tasks to my celery workers, they'll process all the tasks (it takes ~1 hour), and then I'll manually terminate my celery workers.

I want to move towards a system where if a celery worker id 'idle' (which I define as: has 0 active tasks for a time period of timeout_seconds, which I will define beforehand), the worker will be terminated programatically. All workers will have approx the same # of tasks to run, and will all go 'idle' around the same time.

I have code set up that lets me terminate workers, but I am not sure how to detect that a worker is 'idle' and ready for termination. I think I want to use a signal but it doesn't look like there is one that fits my requirement

Answer 1

Here where I work we have a task that is doing basically what you want - automatically scales up/down the cluster depending on the "situation". The key in this process is the Celery inspect/control API, so I suggest you get familiar with it. This is an area that is not well-documented so start with the following:

insp = celery_app.control.inspect()
active_queues = insp.active_queues()
# Note: between these two calls some nodes may shut down and disappear
# from the dictionary so may need to deal with this...
active_stats = insp.active()

You can do this in a separate IPython session while your Celery cluster runs tasks, and look at what is there...