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→An Overview of Network Load Balancing Clusters
Network Load Balancing assigns a virtual IP address to the cluster. When a client request arrives at the cluster this virtual IP address is mapped to the real address of a specific node in the cluster based on configuration settings and server availability. When a server fails, traffic is diverted to another server in the cluster. When the failed node is brought back online it is then re-assigned a share of the load. From a user perspective the load balanced cluster appears to all intents and purposes as a single server represented by one or more virtual IP addresses.
The failure of a node in a cluster is detected by the transmission absence of ''heartbeats'' by each from that node. If a node fails to transmit a heartbeat packet for a designated period of time , that node is assumed to have failed and the remaining nodes takeover the work load of the failed server.
Nodes in a Network Load Balanced cluster typically do not share data, instead each storing a local copy of data. Under such a scenario the cluster is referred to as a ''farm''. This approach is ideal for load balancing of web servers where the same static web site data is stored on each node. In an alternative configuring, referred to as a ''pack'' the nodes in the cluster all access shared data. In this scenario the data is partitioned such that each node in the cluster is responsible for accessing different parts of the shared data. This is commonly used with database servers, with each node having access to different parts of the database data with no overlap (a concept also known as ''shared nothing'').
