Flask At Scale Tutorial at PyCon 2016

This repository contains the companion code to my PyCon 2016 "Flask At Scale" class.

IMPORTANT NOTE: The initial commit in this repository has a version of this application that has a few scalability problems discussed during class. These problems are addressed in subsequent commits.

Installation

All the code and examples were tested on Python 3.5. Older versions of Python including 2.7 will likely work as well.

As usual, create a virtual environment and install the requirements with pip.

pip install -r requirements.txt

Running

The application uses Flask-Script to simplify common tasks such as creating the database and starting a development server. Right after you install the application, you need to create a database for it with this command:

python manage.py createdb

After that, you can run the application with the following command:

python manage.py runserver

You can add --help to see what other start up options are available.

The second component is a message queue, which you need to run as a service. By default, a Redis server running on localhost on the default port is assumed. If you want to use a different message queue, or a different configuration for Redis, then set the CELERY_BROKER_URL environment variable to the message queue connection URL. See the Celery documentation for information on connection URLs.

The final component of this application is the Celery workers, which must be started after the message queue is running with the following command:

python manage.py celery

If you want to have more verbose output from the workers you can add --loglevel=info to the command above.

Usage

That application allows multiple users to chat online. You can launch the application on your browser by typing http://127.0.0.1:5000 on the address bar.

Since authentication is not a topic in this class, I've decided to use a simplified flow that combines the registration and login forms in one. If you are a new user, enter your chosen nickname and password to register. If the nickname was not seen before the server will register you. If you are a returning user, provide your login in the same form. If the nickname is registered then the password will be validated.

Once you are logged in you can type messages in the bottom text entry field, and these messages will be seen by all other users. You can use simple MarkDown formatting to add style to your messages. If you enter any links as part of your message, these will be shown in expanded form below the message.