Building a web server cluster, how?

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http://serverfault.com – I am a student in IT and I have been asked to build a web server cluster for multiple websites. After 2 weeks of searching, reading and testing, I came here to ask for help. What we want is a cluster of web servers working together in load balancing and fail over. What I have as running test setup now: 2 piranha servers in fail over and load balancing over 3 web servers each (nginx/php5). The problems I encountered: Sessions are not synced. I have tried combining memcache, memcached & repcached, I failed to make php save it's sessions inside memcache No ideas about syncing data over (HowTos)