Question

I’m trying to use celery in my Flask-based web app and monitore it’s state. My idea is to store task’s id in session, and use it for state polling.

Here is content of my tasks.py

from traceback import format_exc
import settings
from celery import Celery, current_task
from celery.utils.log import get_task_logger
from celery.result import AsyncResult

from nimble_auth import make_nimble_req

logger = get_task_logger(__name__)

celery = Celery('tasks')
celery.config_from_object(settings)

@celery.task
def make_work(param1, param2):
    try:
        # work here
        current_task.update_state(state='PROGRESS', meta={'current': page, 'total': total_pages})
    except StandardError:
        logger.error(format_exc())

def get_asynctask(task_id):
    return AsyncResult(task_id)

Except from main app’s file web.py

@app.route('/task_state/<task_id>')
def task_state(task_id):
    return get_asynctask(task_id).state # from task.py

@app.route('/reset_task')
def reset_task():
    del session['celery_task_id']
    return redirect(url_for('index'))

@app.route('/run')
def run_task():
    task = make_work.delay(1, 2)
    session['celery_task_id'] = task.task_id
    flash('Task submitted OK!')

    return redirect(url_for('index'))

Settings file:

BROKER_URL = 'mongodb://localhost:27017/dramba'
CELERY_RESULT_BACKEND = "mongodb"
CELERY_RESULT_DBURI = 'mongodb://localhost:27017/dramba'

But when I’m trying to get task’s state, I’m getting NotImplementedError: No result backend configured.

Full stacktrace:

Traceback (most recent call last):
  File "/Users/cleg/Projects/Venvs/Dramba/lib/python2.7/site-packages/flask/app.py", line 1701, in __call__
    return self.wsgi_app(environ, start_response)
  File "/Users/cleg/Projects/Venvs/Dramba/lib/python2.7/site-packages/flask/app.py", line 1689, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "/Users/cleg/Projects/Venvs/Dramba/lib/python2.7/site-packages/flask/app.py", line 1687, in wsgi_app
    response = self.full_dispatch_request()
  File "/Users/cleg/Projects/Venvs/Dramba/lib/python2.7/site-packages/flask/app.py", line 1360, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/Users/cleg/Projects/Venvs/Dramba/lib/python2.7/site-packages/flask/app.py", line 1358, in full_dispatch_request
    rv = self.dispatch_request()
  File "/Users/cleg/Projects/Venvs/Dramba/lib/python2.7/site-packages/flask/app.py", line 1344, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/Users/cleg/Projects/GitHub/Dramba/dramba.py", line 13, in task_state
    return get_asynctask(task_id).state
  File "/Users/cleg/Projects/Venvs/Dramba/lib/python2.7/site-packages/celery/result.py", line 284, in state
    return self.backend.get_status(self.id)
  File "/Users/cleg/Projects/Venvs/Dramba/lib/python2.7/site-packages/celery/backends/base.py", line 490, in _is_disabled
    raise NotImplementedError('No result backend configured.  '
NotImplementedError: No result backend configured.  Please see the documentation for more information.

What am I doing wrong?

Answer 1

It seems that Flask itself doesn’t pickup configuration properly from your file. Try specifying it explicitly and see if it helps: http://docs.celeryproject.org/en/latest/userguide/application.html#example-2-using-a-configuration-module

Also, just to be sure, are there any messages on stdout of Flask process?