I have had a lot of experience with clustering and high-availability in Linux, both at a system level and at the application level. I am very familiar with Heartbeat, IPVS and OSPF. We used all 3 for the Singlesnet.com infrastructure. I am also very familiar with F5 Networks BigIP for Layer 7 load balancing.
I have experience with clustering MySQL, Apache & Nginx, Varnish & Squid and Postfix. I have some experience with clustering Asterisk.