Red Hat Application Server, Manual

Page: 248 / 296

240 Chapter 32. Clustering with JOnAS
Figure 32-3. Session Replication
The term session replication is used when the current service state is being replicated across multiple
application instances. Session replication occurs when the information stored in an HttpSession is
replicated from, in this example, one Servlet engine instance to another. This could be data such as
items contained in a shopping cart or information being entered on an insurance application. Anything
being stored in the session must be replicated for the service to failover without a disruption.
The solution chosen for achieving Session replication is called in-memory session-replication. It uses
a group communication protocol written entirely in Java, called
JavaGroups
.
JavaGroups
is a com-
munication protocol based on the concept of virtual synchrony and probabilistic broadcasting.
The following describes the steps for achieving Session replication with JOnAS.
•
mod_jk
is used to illustrate the Session Replication. Therefore, first perform the configuration steps
presented in the section Section 32.2 Load Balancing at the Web Level with mod_jk .
•
On the JOnAS servers, open the
JONAS_BASE/conf/server.xml
file and configure the
ë
context
ì
as described:
ë
Context path="/replication-example" docBase="replication-example"
debug="99" reloadable="true" crossContext="true"
className="org.objectweb.jonas.web.catalina41.JOnASStandardContext"
ì
ë
Logger className="org.apache.catalina.logger.FileLogger"
prefix="localhost_replication_log." suffix=".txt" timestamp="true"/
ì
ë
Valve className="org.apache.catalina.session.ReplicationValve"
filter=".*\.gif;.*\.jpg;.*\.jpeg;.*\.js" debug="0"/
ì
ë
Manager
className="org.apache.catalina.session.InMemoryReplicationManager"
debug="10"
printToScreen="true"
saveOnRestart="false"
maxActiveSessions="-1"
minIdleSwap="-1"