HTTP: The Definitive Guide

Where to Redirect

Servers, proxies, caches, and gateways all appear to clients as servers, in the sense that a client sends them an HTTP request, and they process it. Many redirection techniques work for servers, proxies, caches, and gateways because of their common, server-like traits. Other redirection techniques are specially designed for a particular class of endpoint and are not generally applicable. We’ll see general techniques and specialized techniques in later sections of this chapter.

Web servers handle requests on a per-IP basis. Distributing requests to duplicate servers means that each request for a specific URL should be sent to an optimal web server (the one nearest to the client, or the least-loaded one, or some other optimization). Redirecting to a server is like sending all drivers in search of gasoline to the nearest gas station.

Proxies tend to handle requests on a per-protocol basis. Ideally, all HTTP traffic in the neighborhood of a proxy should go through the proxy. For instance, if a proxy cache is near various clients, all requests ideally will flow through the proxy cache, because the cache will store popular documents and serve them directly, avoiding longer and more expensive trips to the origin servers. Redirecting to a proxy is like siphoning off traffic on a main access road (no matter where it is headed) to a local shortcut.