7.5.2 How HACMP works

There are two main components to the cluster configuration: cluster topology and cluster resources.

The cluster topology describes the underlying framework, that is, the nodes, networks and storage. HACMP uses this framework to keep the other main component, the resources, highly available.

Cluster resources are those components that HACMP can move from node to node (for example, IP addresses, file systems and applications). An "application" in this context is any application that can run on a standalone AIX server; be started and stopped by scripts; and be recovered by a script after an unexpected shutdown. The application and its associated resources is the unit of failover in HACMP.

When a cluster is configured, the cluster topology and resource information is entered on one node. A verification process is then run, and the data is synchronized out to the other nodes defined in the cluster. HACMP keeps this data in its own Object Data Manager (ODM) classes on each node in the cluster.

Although HACMP can be configured or modified from any node in the cluster, it is good practice to perform administrative operations from one node to ensure that HACMP definitions are kept consistent across the cluster, thus preventing a cluster configuration update from multiple nodes, which may result in inconsistent data.

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