TABLE1–1 FeaturesAvailablefor Each Prole (Continued)
Feature DeveloperProle ClusterProle
EnterpriseProle(not
availablewithSun GlassFish
CommunicationsServer)
SecurityManager Disabled Enabled Enabled
HADB Notavailable Not available Available
Loadbalancing Notavailable Available Available
Nodeagents Notavailable Available Available
Cluster
Acluster is a named collection of server instances sharing the same set of applications,
resources,and conguration information. A server instance can belong to exactly one cluster. A
clusterfacilitates server instance load-balancing through distribution of a load across multiple
machines.A cluster facilitates high availability through instance-level failover. From an
administrativeperspective, 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.
Horizontalscaling is achieved by adding Enterprise Server instances to a cluster, thereby
increasingthe capacity of the system. It is possible to add Enterprise Server instances to a cluster
withoutdisrupting service. The HTTP,RMI/IIOP,and JMS load balancing systems distribute
requeststo healthy Enterprise Server instances in the cluster.
HighAvailability - Availabilityallows for failover protection of Enterprise Server instances in a
cluster.If one application server instance goes down, another Enterprise Server instance takes
overthe sessions that were assigned to the unavailable server. Session information is stored
usingthe session replication feature or by using the high-availability database (HADB). HADB
supportsthe persistence of HTTP sessions and stateful session beans.
Node Agent
Alightweight agent (e.g. hosting a JMX runtime only) is required on each node in the domain
tofacilitate remote lifecycle management of instances. Its primary purpose is to start, stop, and
createserver instances as instructed by the DAS. The Node Agent also acts as a watchdog and
restartsfailed processes. Like the DAS, the Node Agent should only be required for certain
administrativeoperations and should not be expected to be highly available. However, the Node
Agentis an “always on” component, and must be congured to be started by the native O/S
nodebootstrap (e.g. Solaris/Linux inetd, or as a Windows service). A Node Agent is not
requiredfor the DAS.
EnterpriseServer Concepts
SunGlassFishEnterprise Ser ver2.1 Administration Guide • December 200828