Clusters work to provide fault tolerance to a group of systems so that the services they provide are always available—or are unavailable for the least possible amount of time. Clusters also provide a single public-facing presence for a set of systems, which means end users and others who take advantage of the resources the cluster members provide don’t know the cluster comprises more than one machine. They see only a single, unified presence on the network. The dirty work of spreading the load among multiple machines is done behind the scenes by clustering software.
Microsoft provides two distinct types of clustering with Windows Server 2003.
These types of clusters allow for the high availability of services that rely on the TCP/IP protocol. You can have up to 32 machines running any edition of Windows Server 2003 and Windows 2000 Server (with one minor exception, covered later in this chapter) participating in an NLB cluster.
Server clusters are the “premium” variety of highly available machines and consist of servers that generally can migrate workloads and processes across all members of the cluster (with some exceptions, as you’ll see later in this chapter). Failed members of the cluster are automatically detected and the work being performed thereon is moved to other, functional members of the cluster. True server clusters are supported in only the Enterprise and Datacenter editions ...