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Load-balancing is a topic that comes up often with GlassFish users and Markus has posted a piece covering both proxying and load-balancing.
He covers Unix techniques such as iptables, authbind and Apache mod_proxy as both a reverse-proxy or rewriting engine but also the Jsvc utility. He also touches on different load-balancing options: Oracle GlassFish Server, mod_jk, and mod_proxy_balancer. Feel free to share your load-balancing experiences on his blog.