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ChatApp

A small functional person-to-person message center application built using Django. It has a REST API and uses WebSockets to notify clients of new messages and avoid polling.

Architecture

  • When a user logs in, the frontend downloads the user list and opens a Websocket connection to the server (notifications channel).
  • When a user selects another user to chat, the frontend downloads the latest 15 messages (see settings) they've exchanged.
  • When a user sends a message, the frontend sends a POST to the REST API, then Django saves the message and notifies the users involved using the Websocket connection (sends the new message ID).
  • When the frontend receives a new message notification (with the message ID), it performs a GET query to the API to download the received message.

Scaling

Requests

"Because Channels takes Django into a multi-process model, you no longer run everything in one process along with a WSGI server (of course, you’re still free to do that if you don’t want to use Channels). Instead, you run one or more interface servers, and one or more worker servers, connected by that channel layer you configured earlier."

In this case, I'm using the In-Memory channel system, but could be changed to the Redis backend to improve performance and spawn multiple workers in a distributed environment.

Please take a look at the link below for more information: https://channels.readthedocs.io/en/latest/introduction.html

  • use redis as the channel layer backing store. for more information, please check channels_redis

Database

For this demo, I'm using a simple MySQL setup. If more performance is required, a MySQL cluster / shard could be deployed.

PD: I'm using indexes to improve performance.

Assumptions

Because of time constraints this project lacks of:

  • User Sign-In / Forgot Password
  • User Selector Pagination
  • Good Test Coverage
  • Better Comments / Documentation Strings
  • Frontend Tests
  • Modern Frontend Framework (like React)
  • Frontend Package (automatic lintin, building and minification)
  • Proper UX / UI design (looks plain bootstrap)

Run

  1. move to project root folder

  2. Create and activate a virtualenv (Python 3)

python -m venv venv
./venv/scripts/activate
  1. Install requirements
pip install -r requirements.txt
  1. Create a MySQL database
CREATE DATABASE chat CHARACTER SET utf8;
  1. Start Redis Server
redis-server
  1. Init database
./manage.py migrate
  1. Run tests
./manage.py test
  1. Create admin user
./manage.py createsuperuser
  1. Run development server
./manage.py runserver

To override default settings, create a local_settings.py file in the chat folder.

Message prefetch config (load last n messages):

MESSAGES_TO_LOAD = 15