Django+Celery in Heroku not executing async task - django

Question

I have Django+Celery in Heroku, and Celery is set up as:
import djcelery
djcelery.setup_loader()
BROKER_URL = "django://" # tell kombu to use the Django database as the message queue
CELERYBEAT_SCHEDULER = 'djcelery.schedulers.DatabaseScheduler'
CELERY_RESULT_BACKEND = 'djcelery.backends.database:DatabaseBackend'
CELERY_ALWAYS_EAGER = False
CELERY_TIMEZONE = 'Europe/Madrid'
I have 2 tasks defined in tasks.py, one periodic and another that is executed on asynchronous calls:
#task
def test_one_shot():
print "One shot"
#periodic_task(run_every=crontab(minute="*/5"))
def test_periodic():
print "Periodic"
Heroku is configured with a main web worker and a auxiliar worker:
web: gunicorn config.wsgi:application ON
worker: python manage.py celery worker -B -l info ON
With this setup, I run the test_one_shot task as follows:
test_one_shot.apply_async(eta=datetime.now()+timedelta(minutes=2))
And although it appears as registered in the heroku logs:
Received task: test.tasks.test_one_shot[f29c609d-b6e8-45d4-808d-2ca690f029af] eta:[2016-08-07 00:09:30.262362+02:00]
It never executes. On the other hand, the periodic task test_periodic is executed as expected. What am I doing wrong?
Thanks!
EDIT: The task was executed was not appearing in the logs due a datetime time aware issue. However when the task is programmatically called, it is never executed.

Answer 1

I end up changing the celery backend to use RabbitMQ in Heroku following this guide, and the problem get solved.
Basically, I installed RabbitMQ on Heroku:
$ heroku addons:add cloudamqp
And set the new configuration for it:
import djcelery
djcelery.setup_loader()
CELERY_TIMEZONE = 'Europe/Madrid'
BROKER_URL = env("CLOUDAMQP_URL", default="django://")
BROKER_POOL_LIMIT = 1
BROKER_CONNECTION_MAX_RETRIES = None
CELERY_TASK_SERIALIZER = "json"
CELERY_ACCEPT_CONTENT = ["json", "msgpack"]
CELERYBEAT_SCHEDULER = 'djcelery.schedulers.DatabaseScheduler'
CELERY_ALWAYS_EAGER = False
if BROKER_URL == "django://":
INSTALLED_APPS += ("kombu.transport.django",)