Event-Driven Architecture with WebSockets & Redis Pub/Sub

Modern real-time applications—like live auctions, chat platforms, and order tracking—require bidirectional event streaming between server and clients.

1. Scaling WebSockets Horizontally

A single WebSocket server can hold thousands of persistent TCP connections, but scaling across multiple node instances requires a centralized message broker like Redis Pub/Sub.

// Redis Pub/Sub Adapter for WebSocket Broadcast
const pub = redis.duplicate();
const sub = redis.duplicate();

sub.subscribe('order_updates', (message) => {
  const event = JSON.parse(message);
  io.to(event.channel).emit('event', event.payload);
});

2. Handling Reconnections & State Sync

Clients can disconnect unexpectedly. Implement sequence numbers and event replay buffers so reconnected clients resume without missing updates.

Always authorize WebSocket handshake tokens using JWT query parameters or initial HTTP upgrade headers.