How do I properly implement Apache Solr in a clustered Magento environment?

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http://serverfault.com – I'm currently working with a Magento Enterprise 1.12 installation running on a pair of clustered Apache web servers. Both of my web servers draw from their own databases on separate servers which are clustered in a Master-Master MySQL configuration. My problem is that I'm attempting to introduce Solr 3.6.1 into the picture and I'm somewhat unsure of how to properly add it to my cluster. Should I be able to set up one instance of Solr(perhaps on a different server) and point both sites to it or do I need a stand alone instance of Solr for both servers? Do I need two instances of Solr configure (HowTos)