FastAPI Backend Development Bootcamp · Lesson

WebSockets for Real-Time Communication

Build real-time features in FastAPI with WebSockets: accept connections, exchange messages, broadcast to many clients, and handle disconnects cleanly using async patterns.

WebSockets for Real-Time Communication is a free FastAPI Backend Development Bootcamp lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the FastAPI Backend Development Bootcamp learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

From Request/Response to Real-Time

Regular HTTP is request/response: the client asks, the server answers, the connection closes. WebSockets keep a single connection open for full-duplex, real-time messaging. Perfect for chat, live dashboards, and notifications.

Why Async Fits WebSockets

A WebSocket connection lives a long time and is mostly idle waiting for messages. FastAPI's async model lets one worker handle thousands of concurrent connections without blocking.

A Minimal WebSocket Endpoint

Declare a @app.websocket route. Accept the connection, then loop receiving and sending messages.

from fastapi import FastAPI, WebSocket

app = FastAPI()

@app.websocket('/ws')
async def ws(websocket: WebSocket):
    await websocket.accept()
    while True:
        msg = await websocket.receive_text()
        await websocket.send_text(f'echo: {msg}')

Sending JSON

You can exchange structured data with receive_json and send_json instead of raw text.

data = await websocket.receive_json()
await websocket.send_json({'received': data, 'status': 'ok'})

Handling Disconnects

Clients drop off. Catch WebSocketDisconnect to clean up resources instead of crashing the handler.

from fastapi import WebSocketDisconnect

try:
    while True:
        await websocket.receive_text()
except WebSocketDisconnect:
    print('client left')

A Connection Manager

To broadcast, track active connections in a manager class. Add on connect, remove on disconnect.

class Manager:
    def __init__(self):
        self.active = []
    async def connect(self, ws):
        await ws.accept()
        self.active.append(ws)
    def disconnect(self, ws):
        self.active.remove(ws)

Broadcasting to Everyone

Loop the active connections and send each one the message. This is the core of a chat room.

async def broadcast(self, message):
    for connection in self.active:
        await connection.send_text(message)

Broadcast Logic in Plain Python

The manager is just list bookkeeping. Here is the connect/disconnect/broadcast flow simulated synchronously.

active = []
def connect(c): active.append(c)
def disconnect(c): active.remove(c)
def broadcast(msg): return [f'{c}<-{msg}' for c in active]
connect('alice'); connect('bob')
print(broadcast('hi'))
disconnect('alice')
print(broadcast('bye'))

A Chat Room Endpoint

Combine the pieces: connect, broadcast each received message, and disconnect on drop.

manager = Manager()

@app.websocket('/chat')
async def chat(ws: WebSocket):
    await manager.connect(ws)
    try:
        while True:
            text = await ws.receive_text()
            await manager.broadcast(text)
    except WebSocketDisconnect:
        manager.disconnect(ws)

Scaling Beyond One Process

An in-memory manager only knows connections on its worker. To broadcast across multiple workers or servers, use a pub/sub backend like Redis to fan out messages.

Security and Limits

Protect WebSocket endpoints:

Authenticate during the handshake (e.g. token in query or header).
Validate and size-limit incoming messages.
Heartbeat/ping to detect dead connections.

Quick Check

Why does an in-memory connection manager fail to broadcast correctly when you run several Uvicorn workers?

Recap

You added real-time communication:

Accepted WebSocket connections and exchanged text/JSON.
Handled WebSocketDisconnect cleanly.
Built a connection manager to broadcast to many clients.
Learned to scale with Redis pub/sub and to secure connections.

Frequently asked questions

Is the “WebSockets for Real-Time Communication” lesson free?

Yes — the full text of “WebSockets for Real-Time Communication” is free to read here on the web, and the FastAPI Backend Development Bootcamp course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the FastAPI Backend Development Bootcamp course, upgrade to CoddyKit PRO.

What will I learn in “WebSockets for Real-Time Communication”?

Build real-time features in FastAPI with WebSockets: accept connections, exchange messages, broadcast to many clients, and handle disconnects cleanly using async patterns. You practise FastAPI Backend Development Bootcamp with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start FastAPI Backend Development Bootcamp?

No prior experience is required. FastAPI Backend Development Bootcamp on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “WebSockets for Real-Time Communication” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this FastAPI Backend Development Bootcamp lesson?

Yes. Every FastAPI Backend Development Bootcamp lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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