Sun Microsystems 820433510 manual Cluster, Node Agent, Features Available for Each Profile

Enterprise Server Concepts

TABLE 1–1Features Available for Each Profile		(Continued)
				Enterprise Profile (not
				available with Sun GlassFish
Feature	Developer Profile		Cluster Profile	Communications Server)
Security Manager	Disabled		Enabled	Enabled
HADB	Not available		Not available	Available
Load balancing	Not available		Available	Available
Node agents	Not available		Available	Available

Cluster

A cluster is a named collection of server instances sharing the same set of applications, resources, and configuration information. A server instance can belong to exactly one cluster. A cluster facilitates server instance load-balancing through distribution of a load across multiple machines. A cluster facilitates high availability through instance-level failover. From an administrative perspective, a cluster represents a virtualized entity in which operations on a cluster (e.g. deployment of an application) act on all instances that make up the cluster.

Horizontal scaling is achieved by adding Enterprise Server instances to a cluster, thereby increasing the capacity of the system. It is possible to add Enterprise Server instances to a cluster without disrupting service. The HTTP, RMI/IIOP, and JMS load balancing systems distribute requests to healthy Enterprise Server instances in the cluster.

High Availability - Availability allows for failover protection of Enterprise Server instances in a cluster. If one application server instance goes down, another Enterprise Server instance takes over the sessions that were assigned to the unavailable server. Session information is stored using the session replication feature or by using the high-availability database (HADB). HADB supports the persistence of HTTP sessions and stateful session beans.

Node Agent

A lightweight agent (e.g. hosting a JMX runtime only) is required on each node in the domain to facilitate remote lifecycle management of instances. Its primary purpose is to start, stop, and create server instances as instructed by the DAS. The Node Agent also acts as a watchdog and restarts failed processes. Like the DAS, the Node Agent should only be required for certain administrative operations and should not be expected to be highly available. However, the Node Agent is an “always on” component, and must be configured to be started by the native O/S node bootstrap (e.g. Solaris/Linux inetd, or as a Windows service). A Node Agent is not required for the DAS.

28 Sun GlassFish Enterprise Server 2.1 Administration Guide • December 2008