Clustering JBoss AS 7 Applications - JBoss AS 7 Development - page 320

When using mod_cluster , you can dynamically add or remove nodes to your
cluster, because cluster nodes are discovered through an advertising mechanism.
In practice, the mod_cluster libraries on the httpd side send UDP messages on a
multicast group, which is subscribed by AS7 nodes. This allows AS7 nodes the auto-
matic discovery of httpd proxies where application lifecycle notifications are sent.
The next diagram illustrates this concept better:
Installing mod_cluster
The mod_cluster module is implemented as a core AS 7 module, which is a part
of the distribution, on the httpd side as a set of libraries installed on the Apache web
server.
On the JBoss AS 7 side, you can find already bundled the mod_cluster module's
subsystem as part of the clustered configuration file. You can locate it either in the
standalone-ha.xml file or in the standalone-full-ha.xml (and of course in
the domain.xml file) configuration file:
<subsystem
xmlns="urn:jboss:domain:modcluster:1.0">
<mod-cluster-config
advertise-socket="modcluster"/>
</subsystem>
The subsystem contains just a bare-bones configuration that references its socket
binding through the advertise-socket element: