In this article, I will explain how to use Celery with a Flask application. Celery requires a broker to run. The most famous of the brokers is Redis. So to start using Celery with Flask, first we will have to setup the Redis broker.
Redis can be downloaded from their site http://redis.io. I wrote a script that simplifies downloading, building and running the redis server.
When the above script is ran from the first time, the redis folder doesn’t exist so it downloads the same, builds it and then runs it. In subsequent runs, it will skip the downloading and building part and just run the server.
Now that the redis server is running, we will have to install its Python counterpart.
After the redis broker is set, now its time to setup the celery extension. First install celery by using
pip install celery. Then we need to setup celery in the flask app definition.
Now that Celery is setup on our project, let’s define a sample task.
Now to run the celery workers, execute
That should be all. Now to run our little project, we can execute the following script.
If you are wondering how to run the same on Heroku, just use the free heroku-redis extension. It will start the redis server on heroku. Then to run the workers and app, set the Procfile as –
Then set the heroku.sh as –
That’s a basic guide on how to run a Flask app with Celery and Redis. If you want more information on this topic, please see my post Ideas on Using Celery in Flask for background tasks.