About Clustering

Important   The clustering features described in this section are available only with Windows 2000 Advanced Server.

This section introduces the concepts of clustering, fault tolerance, load balancing, and replication. For sites with multiple servers, proper fault tolerance and load balancing result in enhanced performance.

Clustering

Clustering allows multiple servers to be connected through clustering software so that they appear as one computer to users. This connection allows them to utilize features that are not available with stand-alone server nodes, such as failover and load balancing. Server clusters can also share clustered disks containing important information such as a database.

Fault Tolerance

Fault tolerance means that if one server node stops working, another server node can immediately pick up the request load with minimal disruption to users. The process by which the workload of one server node is automatically transferred over to another node is called failover. The process by which the load is restored to the failed server node after it is back online is called failback.

Load Balancing

Load balancing means that two or more servers can support larger amounts of activity by distributing the request load between them so that no one server node is overloaded or underutilized. Server clusters provide static load balancing by the assignment of Web or FTP sites to a specific preferred server node, either manually or programmatically. Network Load Balancing clusters provide load balancing by distributing client connections among multiple server nodes.

Note   Typically, clusters are configured for both load balancing and fault tolerance.

Replication

Replication involves copying content and configuration settings from one server to other servers so that all servers can offer the same resources to users. Replication of configuration settings is necessary for all clusters, whether they share content or not. Replication of content is not necessary for clusters that share a data storage device such as a disk drive. Many clustering applications support replication of both content and configuration settings. IIS provides a utility to replicate configuration settings from one computer to any number of other computers. For details on using this utility see Replication and Clustering in IIS.

Basic Server Cluster Configurations

The following diagram shows a basic Server cluster configuration. Each server node has a local disk which can contain information specific to the node. Both nodes share resources on a hard disk, although only one node at a time can access resources on the disk. The nodes can be configured to use a private interconnect dedicated to cluster communication, or all network communication (including client and internal cluster communication) can take place on the same network connection. This configuration (minus the private interconnect) is necessary for all of the replication and clustering features available in IIS when deployed in a Server cluster. The cluster structure makes load balancing, failover and failback possible.

Cluster Diagram


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