WebSockets are a modern protocol that allows a web application to have persistent, duplex, long-living connections to servers, similar to real TCP connections (and they are, under the hood, pretty normal TCP connections).

WebSockets use the special URL scheme ws:// (or wss:// for secure), and you will see that in your browser error console if you try to run a WebSocket-opening web application from an Nginx-powered server.

The philosophy behind WebSockets directly conflicts with the buffered-reverse proxy idea that is the foundation of Nginx as a web accelerator. See the previous chapter for the comprehensive introduction into what makes Nginx fast. Fortunately, modern Nginx is so much more than just a simple reverse proxy. It has so much to offer that even without the buffering and cheap connection pools, it is too valuable to ditch because of WebSockets. And since version 1.3.13, which was released almost 3 years ago, in early 2013, Nginx has had special...