Background Tasks in Python with RQ
Last updated 07 May 2015
RQ (Redis Queue) makes it easy to add background tasks to your Python applications on Heroku. RQ uses a Redis database as a queue to process background jobs. To get started using RQ, you need to configure your application and then run a worker process in your application.
If you have questions about Python on Heroku, consider discussing it in the Python on Heroku forums. Both Heroku and community-based Python experts are available.
To setup RQ and its dependencies, install it using pip:
$ pip install rq Downloading/unpacking rq Downloading rq-0.1.2.tar.gz Running setup.py egg_info for package rq ... Successfully installed rq
Next, record the new modification to your application’s
$ pip freeze > requirements.txt
Create a worker
Now that we have everything we need to create a worker process, let’s create one.
Create a file called
worker.py. This module will listen to queued tasks and process them as they are received.
import os import redis from rq import Worker, Queue, Connection listen = ['high', 'default', 'low'] redis_url = os.getenv('REDISTOGO_URL', 'redis://localhost:6379') conn = redis.from_url(redis_url) if __name__ == '__main__': with Connection(conn): worker = Worker(map(Queue, listen)) worker.work()
Now you can run your new worker process:
$ python worker.py
To send a job to your new Redis Queue, you need to send your jobs to Redis in your code. Let’s pretend we have a blocking function in an external module,
import requests def count_words_at_url(url): resp = requests.get(url) return len(resp.text.split())
In your application, create a RQ queue:
from rq import Queue from worker import conn q = Queue(connection=conn)
And enqueue the function call:
from utils import count_words_at_url result = q.enqueue(count_words_at_url, 'http://heroku.com')
The blocking function will automatically be executed in the background worker process.
To deploy your new worker system to Heroku, you need to add the worker process to the Procfile in the root of the project.
worker: python worker.py
Additionally, provision an instance of Redis with the Redis To Go addon and deploy with a
$ heroku addons:create redistogo ----> Adding redistogo to secret-samurai-42... done, v10 (free) $ git push heroku master Counting objects: 5, done. Delta compression using up to 4 threads. ...
Once everything’s pushed up, scale your workers according to your needs:
$ heroku scale worker=1 Scaling worker processes... done, now running 1
View worker process output by filtering the logs with the
-p flag and the name of the
worker process type.
$ heroku logs -t -p worker
The worker process can be manually invoked for further isolation.
$ heroku run worker Running worker attached to terminal... up, run.1