[zapperdapper]

You could start by taking a look at the Squid web site (http://www.squid-cache.org). Also the HAProxy web site (http://www.haproxy.org). There's some useful background info there. There's also a commercial entity behind HAProxy with some additional info (https://www.haproxy.com). A nice intro to HAProxy here: https://www.digitalocean.com/community/tutorials/an-introduc...

Also take a look at the Wikipedia pages for Squid and HAProxy.

With regards books, the ones I looked at seemed a bit dated.