HTTP is request-response. Client asks, server answers.

WebSocket: Bi-directional. Server pushes updates without client asking.

Use Cases

• Live chat
• Real-time notifications
• Collaborative editing (Google Docs style)
• Live dashboards (stock prices, analytics)

Socket.IO Implementation

Server (Node.js):

const io = require('socket.io')(server);

io.on('connection', (socket) => {
  console.log('User connected:', socket.id);
  
  socket.on('message', (data) => {
    // Broadcast to all users
    io.emit('message', data);
  });
  
  socket.on('disconnect', () => {
    console.log('User disconnected:', socket.id);
  });
});

Client (React):

import io from 'socket.io-client';

const socket = io('https://api.example.com');

socket.on('message', (data) => {
  setMessages(prev => [...prev, data]);
});

function sendMessage(text) {
  socket.emit('message', { text, user: currentUser });
}

Scaling WebSockets

Problem: 10,000 concurrent connections on 1 server.

Solution: Redis pub/sub for multi-server sync.

const redis = require('redis');
const sub = redis.createClient();
const pub = redis.createClient();

// Server 1 publishes
pub.publish('chat', JSON.stringify({ text: 'Hello' }));

// Server 2 receives
sub.subscribe('chat');
sub.on('message', (channel, message) => {
  io.emit('message', JSON.parse(message));
});

Result: 50,000+ concurrent connections across 5 servers.

Performance Metrics

• Connection latency: 40ms
• Message delivery: 15ms
• 10,000 messages/sec throughput

Want real-time features in your app?
Build with WebSockets