Celery with RabbitMQ: AttributeError: 'DisabledBackend' object has no attribute '_get_task_meta_for'

Question

I'm running the First Steps with Celery Tutorial.

We define the following task:

from celery import Celery

app = Celery('tasks', broker='amqp://guest@localhost//')

@app.task
def add(x, y):
    return x + y

Then call it:

>>> from tasks import add
>>> add.delay(4, 4)

But I get the following error:

AttributeError: 'DisabledBackend' object has no attribute '_get_task_meta_for'

I'm running both the celery worker and the rabbit-mq server. Rather strangely, celery worker reports the task as succeeding:

[2014-04-22 19:12:03,608: INFO/MainProcess] Task test_celery.add[168c7d96-e41a-41c9-80f5-50b24dcaff73] succeeded in 0.000435483998444s: 19 

Why isn't this working?

Answer 1

Just keep reading tutorial. It will be explained in Keep Results chapter.

To start Celery you need to provide just broker parameter, which is required to send messages about tasks. If you want to retrieve information about state and results returned by finished tasks you need to set backend parameter. You can find full list with description in Configuration docs: CELERY_RESULT_BACKEND.

Answer 2

I suggest having a look at: http://www.cnblogs.com/fangwenyu/p/3625830.html

There you will see that instead of

app = Celery('tasks', broker='amqp://guest@localhost//')

you should be writing

app = Celery('tasks', backend='amqp', broker='amqp://guest@localhost//')

This is it.

Answer 3

In case anyone made the same easy to make mistake as I did: The tutorial doesn't say so explicitly, but the line

app = Celery('tasks', backend='rpc://', broker='amqp://')

is an EDIT of the line in your tasks.py file. Mine now reads:

app = Celery('tasks', backend='rpc://', broker='amqp://guest@localhost//')

When I run python from the command line I get:

$ python
>>> from tasks import add
>>> result = add.delay(4,50)
>>> result.ready()
>>> False

All tutorials should be easy to follow, even when a little drunk. So far this one doesn't reach that bar.

Answer 4

in your project directory find the settings file.

then: sudo vim settings.py copy/paste into settings.py: CELERY_RESULT_BACKEND='djcelery.backends.database:DatabaseBackend'

note: this is if you are using django-celery as the backend for storing the messages in the queue.

Answer 5

What is not clear by the tutorial is that the tasks.py module needs to be edited so that you change the line:

app = Celery('tasks', broker='pyamqp://guest@localhost//')

to include the RPC result backend:

app = Celery('tasks', backend='rpc://', broker='pyamqp://')

Once done, Ctrl + C the celery worker process and restart it:

celery -A tasks worker --loglevel=info

The tutorial is confusing in that we're making the assumption that creation of the app object is done in the client testing session, which it is not.