Real-Time Updates

Chat apps, live feeds, notifications, collaborative documents, live scores. Many interview problems require pushing data to clients in real-time. The default model of HTTP is request-response: the client asks, the server answers. Real-time means flipping that model so the server can push data to clients the moment something happens, without waiting to be asked.

This lesson covers the three approaches to real-time communication, when to use each, how to scale persistent connections across many servers, and the fan-out and presence patterns that come up repeatedly in interviews.