How do you implement WebSocket connection management at scale?

Question

Accepted Answer

**WebSocket management** — handle thousands of connections efficiently.

```javascript
const { WebSocketServer } = require("ws");
const Redis = require("ioredis");

// Connection manager
class ConnectionManager {
    constructor() {
        this.connections = new Map();
        this.redis = new Redis();
        this.subscriber = new Redis();
    }

add(userId, ws) {
        if (!this.connections.has(userId)) {
            this.connections.set(userId, new Set());
        }
        this.connections.get(userId).add(ws);
        this.redis.sadd(`user:${userId}:sockets`, ws.id);
    }

remove(userId, ws) {
        const sockets = this.connections.get(userId);
        if (sockets) {
            sockets.delete(ws);
            if (sockets.size === 0) this.connections.delete(userId);
        }
        this.redis.srem(`user:${userId}:sockets`, ws.id);
    }

sendToUser(userId, message) {
        const sockets = this.connections.get(userId);
        if (sockets) {
            const data = JSON.stringify(message);
            sockets.forEach(ws => {
                if (ws.readyState === WebSocket.OPEN) {
                    ws.send(data);
                }
            });
        } else {
            // User on another server — use Redis pub/sub
            this.redis.publish(`user:${userId}`, data);
        }
    }
}
```

**Scaling:**
- Redis pub/sub for cross-server messaging.
- Sticky sessions for connection affinity.
- Health checks / heartbeat.

Node.js: How do you implement WebSocket connection management at scale?