Keepalive integrates well with LVS a great layer 4 solution, but HaProxy is far more flexible as it runs at layer 7 and can do full cookie insertion etc. Many loadbalancing hardware vendors such as Barraccuda, Kemp, ClusterScale, WebMux & Loadbalancer.org use LVS for its high performance. Many use custom proxies for cookie insertion. My company www.Loadbalancer.org uses HaProxy we also provide full root access and source code + 24*7 support.. excuse the shameless plug.

BTW. very nicely written, apache logging config is useful.