1.3.1. Stateless Session Bean in EJB 2.x

Clustering stateless session beans is most probably the easiest case: as no state is involved, calls can be load-balanced on any participating node (i.e. any node that has this specific bean deployed) of the cluster. To make a bean clustered, you need to modify its jboss.xml descriptor to contain a <clustered> tag.

<jboss>    
    <enterprise-beans>      
        <session>        
            <ejb-name>nextgen.StatelessSession</ejb-name>        
            <jndi-name>nextgen.StatelessSession</jndi-name>        
            <clustered>True</clustered>        
            <cluster-config>          
                <partition-name>DefaultPartition</partition-name>          
                <home-load-balance-policy>                 
                    org.jboss.ha.framework.interfaces.RoundRobin          
                </home-load-balance-policy>          
                <bean-load-balance-policy>  
                    org.jboss.ha.framework.interfaces.RoundRobin
                </bean-load-balance-policy>
            </cluster-config>
        </session>
    </enterprise-beans>
</jboss>

Note

The <clustered>True</clustered> element is really just an alias for the <configuration-name>Clustered Stateless SessionBean</configuration-name> element.

In the bean configuration, only the <clustered> element is mandatory. It indicates that the bean works in a cluster. The <cluster-config> element is optional and the default values of its attributes are indicated in the sample configuration above. Below is a description of the attributes in the <cluster-config> element.

partition-name specifies the name of the cluster the bean participates in. The default value is DefaultPartition. The default partition name can also be set system-wide using the jboss.partition.name system property.
home-load-balance-policy indicates the class to be used by the home stub to balance calls made on the nodes of the cluster. By default, the proxy will load-balance calls in a RoundRobin fashion. You can also implement your own load-balance policy class or use the class FirstAvailable that persists to use the first node available that it meets until it fails.
bean-load-balance-policy Indicates the class to be used by the bean stub to balance calls made on the nodes of the cluster. Comments made for the home-load-balance-policy attribute also apply.

In JBoss 3.0.x, each client-side stub has its own list of available target nodes. Consequently, some side-effects can occur. For example, if you cache your home stub and re-create a remote stub for a stateless session bean (with the Round-Robin policy) each time you need to make an invocation, a new remote stub, containing the list of available targets, will be downloaded for each invocation. Consequently, as the first target node is always the first in the list, calls will not seemed to be load-balanced because there is no usage-history between different stubs. In JBoss 3.2+, the proxy families (i.e., the "First AvailableIdenticalAllProxies" load balancing policy, see Section 1.1.3.2, “JBoss AS 3.2+”) remove this side effect as the home and remote stubs of a given EJB are in two different families.