WebSocket in JavaScript: Advanced Real-Time Applications on Node.js

Advanced Work with WebSocket in JavaScript: From Prototype to Production

WebSocket is a protocol that provides full-duplex communication between a client and a server over a single persistent TCP connection. In previous articles, we covered the basics: establishing a connection, sending messages, and simple chats. However, to create truly reliable and scalable real-time applications (online games, trading platforms, collaborative editing systems), it is necessary to master advanced techniques. In this material, we will examine the architecture of a production-grade WebSocket server on Node.js, including scaling, state management, authorization, and error handling.

1. Advanced Server Architecture and Room Management

A simple WebSocket server (based on the ws library) handles all clients in a single global object. In real projects, logical isolation is required — rooms and channels.

Consider an example of an architecture using the RoomManager class:

const WebSocket = require('ws');\n\nclass RoomManager {\n    constructor() {\n        this.rooms = new Map(); // roomName -> Set<WebSocket>\n    }\n\n    join(ws, roomName) {\n        if (!this.rooms.has(roomName)) {\n            this.rooms.set(roomName, new Set());\n        }\n        this.rooms.get(roomName).add(ws);\n        ws.room = roomName; // Save the room on the socket\n    }\n\n    leave(ws) {\n        if (ws.room && this.rooms.has(ws.room)) {\n            this.rooms.get(ws.room).delete(ws);\n            if (this.rooms.get(ws.room).size === 0) {\n                this.rooms.delete(ws.room);\n            }\n        }\n    }\n\n    broadcast(roomName, message, excludeWs = null) {\n        if (!this.rooms.has(roomName)) return;\n        this.rooms.get(roomName).forEach(client => {\n            if (client !== excludeWs && client.readyState === WebSocket.OPEN) {\n                client.send(JSON.stringify(message));\n            }\n        });\n    }\n}\n\n// Usage\nconst wss = new WebSocket.Server({ port: 8080 });\nconst roomManager = new RoomManager();\n\nwss.on('connection', (ws) => {\n    ws.on('message', (data) => {\n        const msg = JSON.parse(data);\n        switch (msg.type) {\n            case 'join':\n                roomManager.join(ws, msg.room);\n                break;\n            case 'message':\n                roomManager.broadcast(ws.room, { user: msg.user, text: msg.text }, ws);\n                break;\n        }\n    });\n\n    ws.on('close', () => roomManager.leave(ws));\n});

This code allows you to create isolated chats or game sessions. Pay attention to handling connection closure — this is critical for preventing memory leaks.

2. Scaling: Clustering and Redis Pub/Sub

A single Node.js process cannot efficiently use more than one CPU core. For scaling, we use the built-in cluster module. However, a problem arises: WebSocket connections are tied to a specific worker. How do you send a message to a user connected to a different worker?

The solution is an external message broker, such as Redis Pub/Sub.

const cluster = require('cluster');\nconst http = require('http');\nconst { Server } = require('ws');\nconst redis = require('redis');\n\nconst REDIS_CHANNEL = 'ws:messages';\n\nif (cluster.isMaster) {\n    // Launch workers by number of cores\n    const numCPUs = require('os').cpus().length;\n    for (let i = 0; i < numCPUs; i++) {\n        cluster.fork();\n    }\n\n    cluster.on('exit', (worker) => {\n        console.log(`Worker ${worker.process.pid} died`);\n        cluster.fork(); // Restart\n    });\n} else {\n    // Worker\n    const server = http.createServer();\n    const wss = new Server({ server });\n\n    // Connect to Redis\n    const pub = redis.createClient();\n    const sub