Logical functions that a node can provide

As we stated before, a cluster is two or more (often many more) computersworking as a single logical system to provide services. Though from the outsidethe cluster may look like a single system, the internal workings to make thishappen can be quite complex.

This figure presents the logical functions that a physical node in a cluster can provide. Remember, these are logical functions; in some cases, multiple logical functions may reside on the same physical node, and in other cases, a logical function may be spread across multiple physical nodes.
Compute node
The compute node is where the real computing is performed. The majority of the nodes in a cluster are typically compute nodes. In order to provide an overall solution, a compute node can execute one or more tasks, based on the scheduling system.

Management node
Clusters are complex environments, and the management of the individual components is very important. The management node provides many capabilities, including:

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  Monitoring the status of individual nodes

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  Issuing management commands to individual nodes to correct problems or to provide commands to perform management functions, such as power on/off

You should not underestimate the importance of cluster management. It is an imperative when trying to coordinate the activities of a large numbers of systems.

Install node
In most clusters, the compute nodes (and other nodes) may need to be reconfigured and/or reinstalled with a new image relatively often. The install node provides the images and the mechanism for easily and quickly installing or reinstalling software on the cluster nodes.

User node
Individual nodes of a cluster are often on a private network that cannot be accessed directly from the outside or corporate network. Even if they are accessible, most cluster nodes would not necessarily be configured to provide an optimal user interface. The user node is the one type of node that is configured to provide that interface for users (possibly on outside networks) who may gain access to the cluster to request that a job be run, or to access the results of a previously run job.

Control node

Control nodes provide services that help the other nodes in the cluster work together to obtain the desired result. Control nodes can provide two sets of functions:

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  Dynamic Host Configuration Protocol (DHCP), Domain Name System (DNS), and other similar functions for the cluster. These functions enable the nodes to easily be added to the cluster and to ensure they can communicate with the other nodes.

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  Scheduling what tasks are to be done by what compute nodes. For instance,if a compute node finishes one task and is available to do additional work, thecontrol node may assign that node the next task requiring work.
  

Storage node
For some applications that are run in a cluster, compute nodes must have fast, reliable, and simultaneous access to the storage system. This can be accomplished in a variety of ways depending on the specific requirements of the application. Storage devices may be directly attached to the nodes or connected only to a centralized node that is responsible for hosting the storage requests.