Windows nt clusters for Availability and Scalabilty

Cluster Service Overview

The Cluster Service controls all aspects of cluster operation on a cluster system. It is implemented as a Windows NT service and consists of six closely related, cooperating components:

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  The Node Manager handles cluster membership, watches the health of other cluster systems.
  
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  Configuration Database Manager maintains the cluster configuration database.
  
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  Resource Manager/Failover Manager makes all resource/group management decisions and initiates appropriate actions, such as startup, restart and failover.
  
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  Event Processor connects all of the components of the Cluster Service, handles common operations and controls Cluster Service initialization.
  
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  Communications Manager manages communications with all other nodes of the cluster.
  
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  Global Update Manager - provides a global update service that is used by other components within the Cluster Service.
  
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  The Resource Monitor, strictly speaking, is not part of the cluster service. It runs in a separate process, or processes, and communicates with the Cluster Service via Remote Procedure Calls (RPC). It monitors the health of each resource via callbacks to the resources. It also provides the polymorphic interface between generic calls like online and the specific online operation for that resource.
  

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  The time service maintains consistent time within the cluster but is implemented as a resource rather than as part of the cluster service itself.
  

We need to elaborate on resources and their properties, before discussing each of the above components in detail.

Resources are implemented as a Dynamically Linked Library (DLL) loaded into the Resource Monitor’s address space. Resources run in the system account and are considered privileged code. Resources can be defined to run in separate processes, created by the Cluster Service when creating resources.

Resources expose a few simple interfaces and properties to the Cluster Service. Resources may depend on other resources. A resource is brought on-line only after the resources it depends on are already on-line, and it is taken off-line before the resources it depends on. We prevent circular dependencies from being introduced. Each resource has an associated list of systems in the cluster on which this resource may execute. For example, a disk resource may only be hosted on systems that are physically connected to the disk. Also associated with each resource is a local restart policy, defining the desired action in the event that the resource cannot continue on the current node. All Microsoft provided resources run in a single process, while other resources will run in at least one other process.

The base product provides resource DLLs for the following resources:

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  Physical disk
  
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  Logical volume (consisting of 1 or more physical disks)
  
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  File and Print shares
  
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  Network addresses and names
  
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  Generic service or application
  
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  Internet Server service