POC Messaging

POC to demonstrate how to set up a websockets API for distrubuted applications.

Overview

Purpose of this project is to demonstrate basic scaffolding for a websocket API, such as connection management and authentication.

1. Authentication: We introduce a short lived token for authentication as browser support for passing headers on the websocket handshake may prevent a authentication headers from being sent. A single use or short lived token that is separate from the user's primary authentication token is appropriate. Here we use a JWT token with 1-minute expiry.

2. Messsaging: Redis Pub/Sub is used to deliver messages. Applications store open sockets in memory, grouped by a username and listen to incoming messages. An application tracking a specific user then forwards the message down the socket on receipt. A pub/sub broker ensures that regardless of where a client connects, we can deliver messages.

Other Concerns

These items are not covered in this POC, but depending on your application's needs, you should take into consideration the following:

1. Depending on the use-case, clients may need access to older/undelivered messages for proper UX. Messages should be timestamped, stored, and queryable if this is required.

2. Delivered messages should be structured and convey meaning. A good example is the Slack API which implement's a type parameter as opposed to enabling multiple websocket APIs to deliver different messages.

3. You will want to budget for a thundering herd of client reconnections should a service go down. Common solutions for this include exponential backoff implemented on the client and rate limiting.

Backend

Backend development server is available at http://localhost:8080

cd messaging
docker-compose -f docker-compose.test.yml up
make dev
pip install -r requirements_dev.txt
python -m messaging

Frontend

To start and access the client application, run the following:

cd web
nvm use
npm install
npm run config:dev
npx npm run start

Client application will be available at http://localhost:4000

Auditing

1. Start up the backend and frontend applications using the instructions above
2. Follow the UI instructions to open a websocket with any username
3. In a separate window/tab/browser, open the webapp and connect using the same username from step 2
4. Submit a message to your username using the command below. Messages should show up on all open web apps.

curl -X POST -d '{"username":"test-user","content":"hi there"}' http://localhost:8080/message