WebSockets Tutorial

1. WebSockets Introduction

Full-duplex vs HTTP request/response, the upgrade handshake, and when (not) to use WebSockets.

2. The WebSocket API

The browser's WebSocket API, a Node.js server with ws, and a complete client+server chat example.

3. Authentication for WebSockets

Getting a token into the handshake without custom headers, validating it server-side, and re-authenticating long-lived connections.

4. Heartbeats and Reconnection

Detecting half-open connections with ping/pong, and a complete client with exponential backoff reconnection.

5. Scaling WebSockets

Why a socket is pinned to one server, solving it with a Redis pub/sub backplane, and rooms/channels.

6. Production Checklist

Load balancer idle timeouts and sticky sessions, connection/file-descriptor limits, and graceful shutdown.

7. WebSocket Interview Questions

Commonly asked WebSocket interview questions with clear, practical answers.