Availability components provide for near-continuous uptime for system service components and application components. The following Java ES availability components are described in this section:
A cluster is a set of loosely coupled computers (cluster nodes) that collectively provides a single client view of services, system resources, and data. Internally, the cluster uses redundant computers, interconnects, data storage, and network interfaces to provide high availability to cluster-based services and data. Sun Cluster software continuously monitors the health of member nodes and other cluster resources, and uses the internal redundancy to provide near-continuous access to these resources even when failure occurs.
The Java ES installer provides the Sun Cluster Core and the Sun Cluster Agents as separately installable components. Additional Sun Cluster agents are available on separate CDs.
Sun Java System High Availability Session Store (HADB) provides a data store that can be used to make application data available even in the case of failure. This capability is especially important for restoring state information associated with a client session. Without this capability, failure during a session requires that all operations be repeated when a the session is re-established.
The following Java ES components provide services that store session state information: Application Server, Access Manager, and Message Queue. However, Application Server is the only one of these components that can use HADB services to maintain session state during failure.
The Java ES installer provides HADB as a single installable component. However, a server and a client subcomponent are both required to provide HADB services.