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    <p>I'm not sure this will answer the question but you might be interested by the way Weblogic Server clustering work under the hood. From the book <a href="http://books.google.com/books?id=Eg8UvYoA4gYC" rel="nofollow noreferrer">Mastering BEA WebLogic Server</a>:</p> <blockquote> <p>[...] WebLogic Server clustering provides a loose coupling of the servers in the cluster. Each server in the cluster is independent and does not rely on any other server for any fundamental operations. Even if contact with every other server is lost, each server will continue to run and be able to process the requests it receives. Each server in the cluster maintains its own list of other servers in the cluster through periodic heartbeat messages. Every 10 seconds, each server sends a heartbeat message to the other servers in the cluster to let them know it is still alive. Heartbeat messages are sent using IP multicast technology built into the JVM, making this mechanism efficient and scalable as the number of servers in the cluster gets large. Each server receives these heartbeat messages from other servers and uses them to maintain its current cluster membership list. If a server misses receiving three heartbeat messages in a row from any other server, it takes that server out of its membership list until it receives another heartbeat message from that server. This heartbeat technology allows servers to be dynamically added and dropped from the cluster with no impact on the existing servers’ configurations.</p> </blockquote>
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    1. POHeartbeat Protocols/Algorithms or best practices
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    1. USPascal Thivent
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    1. COMulticast may not work over a WAN. The advantage of multicast IMO is that you don't need to know how you're sending to (don't need to configure a list of nodes or peers).
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    2. COAgreed with both points. BTW, I should have mentioned that, starting with Weblogic 10, BEA/Oracle supports communication between cluster members using Unicast (which is encouraged) in addition to Multicast.
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    3. CODo you know if it is possible to customize WebLogic's native heartbeat messages, to add some additional information such as current CPU and/or network load? (to allow load-balancing algorithms that use that information to avoid overloading a struggling server with more requests)
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