Front End Gatekeepers
Another approach to load balancing is to have www.example.com be a machine that is actually a front end for a farm of servers. This allows us to have duties divided up between machines on the back end.

Reverse Proxies

Configuring Apache with mod_proxy and mod_rewrite makes for a very versatile http server. There are also a number of well documented uses for Squid and, to lesser extent, Eddie to perform in this role as well.

"Intelligent NAT"

This is a class of products that use Network Address Translation to compute which destination on the back end should receive an incoming connection instead of staticly mapped NAT.

Layer 4 switches

A new class of hardware product that looks up the protocol stack to decide how it should "route" traffic. It's sort of a hybrid reverse proxy, router and switch.

Suppose we have a number of different functionalities at

http://www.example.com/cgi-bin/
http://www.example.com/images/
http://www.example.com/apps/