Quintin Par Quintin Par - 5 months ago 48
Python Question

Retry Celery tasks with exponential back off

For a task like this:

from celery.decorators import task

@task()
def add(x, y):
if not x or not y:
raise Exception("test error")
return self.wait_until_server_responds(


if it throws an exception and I want to retry it from the daemon side, how can apply an exponential back off algorithm, i.e. after
2^2, 2^3,2^4
etc seconds?

Also is the retry maintained from the server side, such that if the worker happens to get killed then next worker that spawns will take the retry task?

Answer

The task.request.retries attribute contains the number of tries so far, so you can use this to implement exponential back-off:

from celery.task import task

@task(bind=True, max_retries=3)
def update_status(self, auth, status):
    try:
        Twitter(auth).update_status(status)
    except Twitter.WhaleFail as exc:
        self.retry(exc=exc, countdown=2 ** self.request.retries)

To prevent a Thundering Herd Problem, you may consider adding a random jitter to your exponential backoff:

import random
self.retry(exc=exc, countdown=int(random.uniform(2, 4) ** self.request.retries))