Dynamically change the periodic interval of celery task at runtime - dynamic

Question

I have a periodic celery task running once per minute, like so:
#tasks.py
#periodic_task(run_every=(crontab(hour="*", minute="*", day_of_week="*")))
def scraping_task():
result = pollAPI()
Where the function pollAPI(), as you might have guessed from the name, polls an API. The catch is that the API has a rate limit that is undisclosed, and sometimes gives an error response, if that limit is hit. I'd like to be able to take that response, and if the limit is hit, decrease the periodic task interval dynamically (or even put the task on pause for a while). Is this possible?
I read in the docs about overwriting the is_due method of schedules, but I am lost on exactly what to do to give the behaviour I'm looking for here. Could anyone help?

Answer 1

You could try using celery.conf.update to update your CELERYBEAT_SCHEDULE.

Answer 2

You can add a model in the database that will store the information if the rate limit is reached. Before doing an API poll, you can check the information in the database. If there is no limit, then just send an API request.
The other approach is to use PeriodicTask from django-celery-beat. You can update the interval dynamically. I created an example project and wrote an article showing how to use dynamic periodic tasks in Celery and Django.
The example code that updates the task when the limit reached:
def scraping_task(special_object_id, larger_interval=1000):
try:
result = pollAPI()
except Exception as e:
# limit reached
special_object = ModelWithTask.objects.get(pk=special_object_id)
task = PeriodicTask.objects.get(pk=special_object.task.id)
new_schedule, created = IntervalSchedule.objects.get_or_create(
every=larger_inerval,
period=IntervalSchedule.SECONDS,
)
task.interval = new_schedule
task.save()
You can pass the parameters to the scraping_task when creating a PeriodicTask object. You will need to have an additional model in the database to have access to the task:
from django.db import models
from django_celery_beat.models import PeriodicTask
class ModelWithTask(models.Model):
task = models.OneToOneField(
PeriodicTask, null=True, blank=True, on_delete=models.SET_NULL
)
# create periodic task
special_object = ModelWithTask.objects.create_or_get()
schedule, created = IntervalSchedule.objects.get_or_create(
every=10,
period=IntervalSchedule.SECONDS,
)
task = PeriodicTask.objects.create(
interval=schedule,
name="Task 1",
task="scraping_task",
kwargs=json.dumps(
{
"special_obejct_id": special_object.id,
}
),
)
special_object.task = task
special_object.save()