How do you scale a MERN real-time app?

Redis pub/sub as the Socket.io adapter allows multiple Node.js instances to broadcast to all connected clients. PM2 cluster mode scales across CPU cores on a single server before needing multiple servers. We design the scaling architecture in the discovery session. Most MERN real-time applications handle their first 12 to 18 months of growth on a single scaled Node.js server before needing horizontal scaling.