flask-redis-docker

An example about how to deploy a Flask application inside a Docker able to perform asynchronous, parallel requests, with the Flask application handled by NGINX/uWSGI.

How it works

Though Python allows asynchronous executions through several techniques, forking asynchronous processes from the uWSGI plugin is not allowed (at least by default), and not recommended (see https://docs.docker.com/config/containers/multi-service_container/). A good solution is to define a worker process within the main processes of the container (i.e. handled through supervisor, used as main process defined in the container's CMD), that is able to perform operations in background.

The repo has two sections, one dedicated to Python 2.7 (based on RedisQueue) and one to Python 3.6 (based on Celery). Both examples use Redis as broker messages.

How to run it

Once you have docker-compose installed, just create the images and the containers through the command:

$ docker-compose up -d

This will create the two containers, the one with the Flask application listening port 5000, and the one with the Redis service (listening port 6379).

$ docker-compose ps
 Name               Command               State               Ports            
-------------------------------------------------------------------------------
redis    docker-entrypoint.sh redis ...   Up      6379/tcp                     
webapp   /entrypoint.sh /start.sh         Up      443/tcp, 0.0.0.0:5000->80/tcp

Once both services are up and running in your localhost, you can submit a long running request asynchronously as follows:

$ curl -X POST -F "duration=20" http://127.0.0.1:5000/long_task

and for a parallelised task:

$ curl -X POST -F "duration=200" http://127.0.0.1:5000/parallel_long_task

Then the outputs can be retrieved as follows:

$ curl -X GET http://127.0.0.1:5000/task/<task_id>

or, in the case of a parallel task:

$ curl -X GET http://127.0.0.1:5000/parallel_task/<task_id>