Cluster; Node Agent - Sun Microsystems GlassFish Enterprise Server 2.1 Administration Manual

Enterprise Server Concepts
TABLE 1–1
Feature
Security Manager
HADB
Load balancing
Node agents

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
Features Available for Each Profile
Developer Profile
Disabled
Not available
Not available
Not available
(Continued)
Cluster Profile
Enabled
Not available
Available
Available
Enterprise Profile (not
available with Sun GlassFish
Communications Server)
Enabled
Available
Available
Available