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 What Is Clustering?

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

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

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)
Clustering Hardware

Clustering Hardware

A typical clustering setup includes:

  • Disks that are shared between nodes

    These are needed if the application uses dynamic data as mail servers or database servers do.

    The shared disks may be shared SCSI disks or a storage area network using Fibre Channel.

  • Extra network connectivity between nodes for monitoring heartbeat status.
  • A method for redirecting incoming requests.

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