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30.2.3. The HA HttpInvoker - Clustered RMI/HTTP Transport

The RMI/HTTP layer allows for software load balancing of the invocations in a clustered environment. An HA capable extension of the HTTP invoker has been added that borrows much of its functionality from the HA-RMI/JRMP clustering.
To enable HA-RMI/HTTP you need to configure the invokers for the EJB container. This is done through either a jboss.xml descriptor, or the standardjboss.xml descriptor. Example 30.3, “A jboss.xml stateless session configuration for HA-RMI/HTTP” shows is an example of a stateless session configuration taken from the org.jboss.test.hello testsuite package.

Example 30.3. A jboss.xml stateless session configuration for HA-RMI/HTTP

<jboss>
    <enterprise-beans>
        <session>
            <ejb-name>HelloWorldViaClusteredHTTP</ejb-name>
            <jndi-name>helloworld/HelloHA-HTTP</jndi-name>
            <invoker-bindings>
                <invoker>
                    <invoker-proxy-binding-name>
                        stateless-httpHA-invoker
                    </invoker-proxy-binding-name>
                </invoker>
            </invoker-bindings>
            <clustered>true</clustered>
        </session>
    </enterprise-beans>
    <invoker-proxy-bindings>
        <invoker-proxy-binding>
            <name>stateless-httpHA-invoker</name>
            <invoker-mbean>jboss:service=invoker,type=httpHA</invoker-mbean>
            <proxy-factory>org.jboss.proxy.ejb.ProxyFactoryHA</proxy-factory>
            <proxy-factory-config>
                <client-interceptors>
                    <home>
                        <interceptor>org.jboss.proxy.ejb.HomeInterceptor</interceptor>
                        <interceptor>org.jboss.proxy.SecurityInterceptor</interceptor>
                        <interceptor>org.jboss.proxy.TransactionInterceptor</interceptor>
                        <interceptor>org.jboss.invocation.InvokerInterceptor</interceptor>
                    </home>
                    <bean>
                        <interceptor>
                            org.jboss.proxy.ejb.StatelessSessionInterceptor
                        </interceptor>
                        <interceptor>org.jboss.proxy.SecurityInterceptor</interceptor>
                        <interceptor>org.jboss.proxy.TransactionInterceptor</interceptor>
                        <interceptor>org.jboss.invocation.InvokerInterceptor</interceptor>
                    </bean>
                </client-interceptors>
            </proxy-factory-config>
        </invoker-proxy-binding>
    </invoker-proxy-bindings>
</jboss>
The stateless-httpHA-invoker invoker-proxy-binding references the jboss:service=invoker,type=httpHA invoker service. This service would be configured as shown below. 
<mbean code="org.jboss.invocation.http.server.HttpInvokerHA"
       name="jboss:service=invoker,type=httpHA">
    <!-- Use a URL of the form
         http://<hostname>:8080/invoker/EJBInvokerHAServlet
         where <hostname> is InetAddress.getHostname value on which the server
         is running.
    -->
    <attribute name="InvokerURLPrefix">http://</attribute>
    <attribute name="InvokerURLSuffix">:8080/invoker/EJBInvokerHAServlet</attribute>
    <attribute name="UseHostName">true</attribute>
</mbean>
The URL used by the invoker proxy is the EJBInvokerHAServlet mapping as deployed on the cluster node. The HttpInvokerHA instances across the cluster form a collection of candidate http URLs that are made available to the client side proxy for failover and/or load balancing.
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