WebSockets, SSE & Polling

A WebSocket starts as an HTTP request that asks to switch protocols, gets `101 Switching Protocols`, and from then on the same TCP connection carries framed messages in both directions for as long as both sides want — which makes every proxy, load balancer and idle timer between them part of the design.

Four ways to get data from a server that has news to a client that only asks: repeated requests, requests the server holds open, a one-way HTTP stream with built-in reconnection, and a bidirectional socket — each trades infrastructure simplicity against latency and directionality.