How to schedule a chain task in celery

Question

I want to run a complex task scheduled by beat. Let us assume the default add/mul tasks are defined.

@app.on_after_configure.connect
def setup_periodic_tasks(sender, **kwargs):
    sender.add_periodic_task(
        crontab(),
        add.s(2,3) | mul.s(2)
    )

But this will return an error in the worker:

NotImplementedError: chain is not a real task

How can I schedule a non trivial task with celery beat?

Answer 1

One way to do that is to schedule your tasks chain in beat_schedule in your celeryconfig, using link option, celery_tasks here is a module name where your tasks are defined

from celery.schedules import crontab
from celery import signature

beat_schedule = {
    'chained': {
        'task': 'celery_tasks.add',
        'schedule': crontab(),
        'options': {
            'queue': 'default',
            'link': signature('celery_tasks.mul',
                        args=(),
                        kwargs={},
                        options={
                            'link': signature('celery_tasks.another_task', 
                                args=(),
                                kwargs={}, 
                                queue='default')
                        },
                        queue='default')
            },
         'args': ()
    }
}