This guide outlines the steps to integrate Celery with a Flask application and monitor tasks using Flower. It covers the setup for development environments, including starting a Redis server, initializing a Flask application, setting up Celery, and using Flower for monitoring.

Create and activate a virtual environment:

py -3 -m venv .venv

.venv\Scripts\activate

Install Flask and all required dependencies:

pip install -r requirements

Run the Flask app with debugging turned on (for autoreload upon changes):

flask --app src/app --debug run

You can now view your app at: http://127.0.0.1:5000/

Set up the Flask application environment variables and start the Flask application using the following commands:

For Windows

$env:FLASK_APP = "src/app.py"

$env:FLASK_ENV = "development"

For Unix/Linux

export FLASK_APP=src/app.py

export FLASK_ENV=development

Note: you can now run flask run or flask run --debug instead of flask --app src/app run --debug

Ensure that the Redis server is running

redis-cli ping

If you do not receive a "PONG" response, start the Redis server

redis-server

Terminal #1: Start Celery

Navigate to the src directory to start the Celery worker

cd src

celery -A app.celery worker --pool=solo --loglevel=info -f logs/celery.log

Terminal #2: Start Flask

Start the Flask shell environment

flask shell

Terminal #3: Monitor Celery with Flower

To monitor Celery tasks and workers, start Flower in a new terminal

celery -A app.celery flower --port=5555

Navigate to http://localhost:5555 to view the dashboard.

Send tasks to Celery in Terminal #2 (Flask)

from app import divide

task = divide.delay(1, 2)

type(task)

print(task.state, task.result)

To monitor the status of a task, use its AsyncResult ID from the Flower dashboard UUID column

from celery.result import AsyncResult

task = AsyncResult(<<AsyncResult ID>>)

task.state

task.result

[x] https://testdriven.io/courses/flask-celery/getting-started/

[ ] https://flask.palletsprojects.com/en/3.0.x/patterns/celery/#integrate-celery-with-flask