Installation guide

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VMware ESX Server Administration Guide
What Is Clustering?
Clustering is simply described as providing a service via a group of servers to get high
availability, scalability or both.
For example, all nodes in a cluster serve a Web site that serves static content. The main
gateway distributes requests to all nodes according to load. It redirects requests to
remaining nodes if one crashes. This gives better availability and better performance.
Network Load Balancing in Windows 200 provides such a service.
Another example of a more complex configuration: A single node serves a database. If
that node crashes, the clustering software must restart the database on another node.
The database application knows how to recover from a crash. In normal operation,
other nodes are used for running other applications. Microsoft Cluster Service and
Veritas Cluster Service provide such a service.
Applications that Can Use Clustering
To take advantage of clustering services, applications need to be clustering aware.
Such applications can be:
• Stateless, as Web servers and VPN servers are.
• With built-in recovery features, like those in database servers, mail servers, file
servers or print servers.
Clustering Software
Available clustering software include:
• Microsoft Clustering Service (MSCS)
Provides fail-over support for 2- to 8-node clusters for applications such as
databases, file servers and mail servers
• Microsoft Network Load Balancing (NLB)
Load balances incoming IP traffic across a cluster of nodes for applications such
as Web servers and terminal services.
• Veritas Clustering Service (VCS)