If you ever had to face HTTP scaling issues, you probably used a caching reverse-proxy like Squid, Apache, Webcache or Varnish.
But although the document is quite old, have you ever looked at the notes about the Varnish architecture ?
Even if you don’t use Varnish, this is worth reading in order to understand what changed since 1970’s and how we really should design applications to wisely use what modern hardware and operating systems have to offer.