Airflow scheduler is throwing out an error - 'DisabledBackend' object has no attribute '_get_task_meta_for' - celery

Question

I am trying to install airflow (distributed mode) in WSL, I got the setup of Airflow webserver, Airflow Scheduler, Airflow Worker, Celery (3.1) and RabbitMQ.
While running the Airflow Scheduler it is throwing out this error (below) even though the backend is set up.
ERROR
Traceback (most recent call last):
File "/usr/local/lib/python3.6/dist-packages/airflow/executors/celery_executor.py", line 92, in sync
state = task.state
File "/usr/local/lib/python3.6/dist-packages/celery/result.py", line 398, in state
return self._get_task_meta()['status']
File "/usr/local/lib/python3.6/dist-packages/celery/result.py", line 341, in _get_task_meta
return self._maybe_set_cache(self.backend.get_task_meta(self.id))
File "/usr/local/lib/python3.6/dist-packages/celery/backends/base.py", line 288, in get_task_meta
meta = self._get_task_meta_for(task_id)
AttributeError: 'DisabledBackend' object has no attribute '_get_task_meta_for'
https://issues.apache.org/jira/browse/AIRFLOW-1840
This is the exact error I am getting but couldn't find a solution.
Result Backend-
result_backend = db+postgresql://postgres:****#localhost:5432/postgres
broker_url = amqp://rabbitmq_user_name:rabbitmq_password#localhost/rabbitmq_virtual_host_name
Help please, gone through almost all the documents but couldn't find a solution

Answer 1

I was facing the same issue on celery version - 3.1.26.post2 (with rabitmq,postgresql and airflow),the reason for this issue is the dictionary used in celery base.py file at(lib/python3.5/site-packages/celery/app/base.py)
does not capture celery backend at key CELERY_RESULT_BACKEND instead it captures at key result_backend.
So the solution here is go to _get_config function available in base.py file at(lib/python3.5/site-packages/celery/app/base.py),at the end of the function before returning dictionary s add the below code.
s['CELERY_RESULT_BACKEND'] = s['result_backend'] #code to be added
return s
This solved the problem.