Running Celery worker inside an app context still raises "working outside of app context" error in task

Question

I am using Miguel Grinberg's article to set up Celery with the app factory pattern in order to send email with Flask-Mail. I've been calling various scripts that use Celery without any issues. However I keep getting Runtime Error: working outside of application context with the following task even though I am running the worker inside an app context. Why am I getting this error? How do I get Flask-Mail to work in Celery?

email.py:

from flask import current_app, render_template
from flask.ext.mail import Message
from . import celery, mail

@celery.task
def send_async_email(msg):
    mail.send(msg)

def send_email(to, subject, template, **kwargs):
    with current_app.test_request_context(): # used app_context() as well.
        msg = Message(current_app.config['PORTAL_MAIL_SUBJECT_PREFIX'] + ' ' +                                       subject,
                  sender=current_app.config['PORTAL_MAIL_SENDER'], recipients=[to])
        msg.body = render_template(template + '.txt', **kwargs)
        msg.html = render_template(template + '.html', **kwargs)
        send_async_email.delay(msg)

__init__.py:

from flask import Flask
from celery import Celery
from flask.ext.mail import Mail
from configuration import config

mail = Mail()
celery = Celery(__name__, broker=config['default'].CELERY_BROKER_URL)

def create_app(config_name):
    app = Flask(__name__)
    app.config.from_object(config[config_name])
    config[config_name].init_app(app)
    mail.init_app(app)
    celery.conf.update(app.config)
    app.register_blueprint(main_blueprint)
    return app

celery_worker.py:

import os
from app import celery, create_app

app = create_app(os.getenv('FLASK_CONFIG') or 'default')
app.app_context().push()

Error:

C:\Python27\Scripts\celery.exe worker -A celery_worker.celery --loglevel=info

[2015-09-30 12:07:34,408: INFO/MainProcess] Received task: app.email.send_async_email[3ec772ff-4767-49cb-90ba-445629da30da]
[2015-09-30 12:07:34,417: ERROR/MainProcess] Task app.email.send_async_email[3ec772ff-4767-49cb-90ba-445629da30da] raised unexpected: RuntimeError('working outside of application context',)
Traceback (most recent call last):
  File "C:\Python27\lib\site-packages\celery\app\trace.py", line 240, in trace_task
    R = retval = fun(*args, **kwargs)
  File "C:\Python27\lib\site-packages\celery\app\trace.py", line 438, in __protected_call__
    return self.run(*args, **kwargs)
  File "<flask_project_path>\app\email.py", line 10, in send_async_email
    mail.send(msg)
  File "C:\Python27\lib\site-packages\flask_mail.py", line 491, in send
    with self.connect() as connection:
  File "C:\Python27\lib\site-packages\flask_mail.py", line 508, in connect
    return Connection(app.extensions['mail'])
  File "C:\Python27\lib\site-packages\werkzeug\local.py", line 338, in __getattr__
    return getattr(self._get_current_object(), name)
  File "C:\Python27\lib\site-packages\werkzeug\local.py", line 297, in _get_current_object
    return self.__local()
  File "C:\Python27\lib\site-packages\flask\globals.py", line 34, in _find_app
    raise RuntimeError('working outside of application context')
RuntimeError: working outside of application context

I have tried:

• Trying to pass the application context to the send_email method.
• Moving the send_async_email method to a tasks.py module where the rest of my celery tasks reside.
• Rendering the templates outside of the email methods and passing them as arguments.

Answer 1

I was able to fix the issue by creating an instance of the flask application locally:

email.py:

from flask import render_template, current_app
from flask.ext.mail import Message
from . import celery, mail, create_app


@celery.task
def send_async_email(msg):
    app = create_app('default' or 'development')  # -> fixed
    with app.app_context():
        mail.send(msg)


def send_email(to, subject, template, **kwargs):
    app = current_app._get_current_object()
    msg = Message(current_app.config['PORTAL_MAIL_SUBJECT_PREFIX'] + ' ' +     subject,
    sender=current_app.config['MAIL_USERNAME'], recipients=[to])
    msg.body = render_template(template + '.txt', **kwargs)
    msg.html = render_template(template + '.html', **kwargs)
    send_async_email.delay(msg)