Celery Task Retry Backoff Jitter

import random

from celery import Celery

app = Celery('shipping', broker='redis://localhost:6379/1')
app.conf.update(
    task_acks_late=True,
    worker_prefetch_multiplier=1,
    task_reject_on_worker_lost=True,
)


class CarrierUnavailable(Exception):
    pass


@app.task(
    bind=True,
    max_retries=5,
    autoretry_for=(CarrierUnavailable,),
    retry_backoff=2,
    retry_backoff_max=600,
    retry_jitter=True,
)
def book_shipment(self, order_id: str, carrier: str):
    try:
        if random.random() < 0.5:
            raise CarrierUnavailable(f'{carrier} api warming up')
        return {'order': order_id, 'carrier': carrier, 'tracking': 'TRK-88'}
    except CarrierUnavailable as exc:
        countdown = min(2 ** self.request.retries * 2, 600)
        countdown += random.uniform(0, countdown * 0.3)
        raise self.retry(exc=exc, countdown=countdown)


@app.task
def shipment_stats():
    inspector = app.control.inspect()
    active = inspector.active() or {}
    reserved = inspector.reserved() or {}
    return {
        'active_tasks': sum(len(w) for w in active.values()),
        'reserved_tasks': sum(len(w) for w in reserved.values()),
    }