Cluster SLSB load balancing.

[gcontini]

Hi!

I'm using jboss 6 and I'm trying to load balance remote ejb calls in a cluster. I want that some of the remote calls are routed on nodes other than the current one. (I have a TimerService deployed as a singleton and i want to load balance the batch load).

I've run into a problem that's documented here:

http://community.jboss.org/wiki/ClusteringFAQ "Why are calls between clustered session beans not load balanced even though load balancing policy is Round Robin?".

I don't want to undeploy some of the ejb from one of the containers, so i wrote my own interceptor as described in the wiki.

{code}

package acme;
import org.jboss.invocation.Invocation;
import org.jboss.invocation.InvokerInterceptor;
public class MyInvokerInterceptor extends InvokerInterceptor {
          @Override
          public boolean hasLocalTarget(final Invocation invocation) {
                    return false;
          }
}

{code}

Then i tried to configure it in standardjboss.xml. I modified the "clustered-stateless-unified-invoker" replacing:

{noformat}

<interceptor call-by-value="false">org.jboss.invocation.InvokerInterceptor</interceptor>
{noformat}

with:

{noformat}

<interceptor call-by-value="false">acme.MyInvokerInterceptor</interceptor>

{noformat}

and i've configured the correct "invoker-proxy-binding-name" in jboss.xml into my application jar, but yet remote calls always choose the same cluster node where they are generated.

I tried a completely different way modifying ejb3-interceptors-aop.xml, commenting out:

{noformat}

<interceptor-ref name="org.jboss.ejb3.remoting.ClusteredIsLocalInterceptor"/>

{noformat}

at this point remote calls are load balanced and everything seem to work fine (in my sample i use no persistence yet) but i get the following exception:

{noformat}

12:48:31,049 ERROR [STDERR] java.lang.RuntimeException: cannot import a transaction context when a transaction is already associated with the thread
12:48:31,050 ERROR [STDERR]           at org.jboss.aspects.tx.TxPropagationInterceptor.invoke(TxPropagationInterceptor.java:62)
12:48:31,050 ERROR [STDERR]           at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
{noformat}

How can i avoid this exception?

Gabriele

[wdfink]

AFAIK, you can not have transactions across different server (my experience is from EJB2).

If you start local without a transaction I suppose it will work.

The default behaviour is to stay local because of a better performance.

[gcontini]

Thank you, you're right starting without a transaction works fine.

To summarize all my previous post i can say:

In order to get the SLSB remote calls load balanced in a cluster you must modify "ejb3-interceptors-aop.xml" under the section "ClusteredStatelessSessionClientInterceptors" commenting out:

<interceptor-ref name="org.jboss.ejb3.remoting.ClusteredIsLocalInterceptor"/>

And you must call the remote bean without an active transaction in context.

The invocation stack can be choosen on a "per session bean"  in jboss.xml:

<session>

                              <ejb-name>RemoteImpl2</ejb-name>

                              <remote-binding>

                                        <interceptor-stack>ClusteredStatelessSessionClientInterceptors</interceptor-stack>

                              </remote-binding>

                              <clustered>true</clustered>

</session>

This strategy requires a modification to a global configuration file. Is there a way to avoid this and do the full configuration inside my ejb jar?

Somebody is trying to do this without success http://community.jboss.org/message/536906