Another way to write clustered singletons

[dimitris]

Just added notifications emitted by the HASingletonDeployer:
http://jira.jboss.com/jira/browse/JBAS-2626
and a BarrierController http://wiki.jboss.org/wiki/Wiki.jsp?page=BarrierController listening to them to control a Barrier.

So services deployed normally inside ./deploy or ./farm that want to be
started/stopped whenever the content of ./deploy-hasingleton/ gets
deployed/undeployed, or else, whenever the current node becomes the
master, need only specify a dependency on the Barrier mbean:

<depend>jboss.ha:service=HASingletonDeployer,type=Barrier</depend>

This provides an alternative to the deploy-hasingleton approach in that we can use farming to distribute the service, while content in deploy-hasingleton must be copied manually on all nodes. On the other hand, the farmed service will be instantiated/created on all nodes, but only started on the master node.

So this is not a replacement, rather one more option for writing clusterred singleton services.

[oglueck]

In http://jboss.org/jbossBlog/blog/dimitris/?permalink=Clustered_Singletons_simplified.txt you state this works for MDBs only as of 4.0.4. I don't see why this should not work with 4.0.3 (but I have not tried). Could you explain?

[brian.stansberry]

Haven't checked, but I would assume because the HASingletonDeployer notifications mentioned in JBAS-2626 were only added in 4.0.4.

[batter]

Is there a list of jmx notifications emitted by services? At one blog I read something like org.jboss.system.server.stopped that will tell you that the jboss kernel stopped; what are the jmx message emitted f.e. by mq and other services ?

[oglueck]

Not only such a list would be interesting. You also must filter them for instance with the DeploymentInfoNotificationFilterFactory. So one must know the possible filter cirteria.

[dimitris]

I had made a start to document this list here:
http://wiki.jboss.org/wiki/Wiki.jsp?page=NotificationsEmittedByJBossMBeans
Obviously we need everyone to contribute to this page.

Another possibility is just configure a NotificationListener to listen for all notifications in the system, boot jboss, take the log and record what you see :)

[dimitris]

And while here, I made this addition to the BarrierController:
http://jira.jboss.com/jira/browse/JBAS-3469
It could be used to control HASingletons that are fully destroyed/created when a node becomes master, rather than just started/stopped.

[oglueck]

By the way, Dimitris, do you know how the deployment of a WAR file is notified? I must create a barrier so I can depend an MBean on it that uses a servlet deployed in that WAR file.

[batter]

"oglueck" wrote:
Not only such a list would be interesting. You also must filter them for instance with the DeploymentInfoNotificationFilterFactory. So one must know the possible filter cirteria.

Definitely; I am trying to add a dependency on the MQ service being started so I know f.e. that my queues and topics are deployed. Finally ran into this barrier discussion and am now playing with using that and then filtering on 'some' mq notification. For the time being I wrote my own bean and playing with it; if people leave me alone today I might do that NotificationListener thingy Dimitris suggested :-)

[oglueck]

You can also try and filter with MBeanServerNotificationFilterFactory for MBean registration notifications. See
http://docs.jboss.org/jbossas/javadoc/4.0.5/system/org/jboss/system/filterfactory/MBeanServerNotificationFilterFactory.html

I am trying to figure out with that one when Axis has registered its JMX bean.

[sebastianlacuesta]

Excellent. I want to call a method of a singleton service. I tried using an RMIAdaptor this way:

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 PrintWriter out = response.getWriter();
 String numero = request.getParameter("numero");
 String mensaje = request.getParameter("mensaje");
 try {
 Context context = new InitialContext();
 RMIAdaptor rmiAdaptor = (RMIAdaptor)context.lookup("jmx/rmi/RMIAdaptor");
 if ((rmiAdaptor != null) && (rmiAdaptor.isRegistered(new ObjectName("poksmedia.mbean:service=MBloxService")))) {
 rmiAdaptor.invoke(new ObjectName("poksmedia.mbean:service=MBloxService"), "sendMessage", new Object[]{numero, mensaje}, new String[]{"java.lang.String", "java.lang.String"});
 out.print("El mensaje se envió correctamente (creo).");
 }
 } catch (NamingException e) {
 // TODO Auto-generated catch block
 e.printStackTrace();
 } catch (MalformedObjectNameException e) {
 // TODO Auto-generated catch block
 e.printStackTrace();
 } catch (NullPointerException e) {
 // TODO Auto-generated catch block
 e.printStackTrace();
 } catch (InstanceNotFoundException e) {
 // TODO Auto-generated catch block
 e.printStackTrace();
 } catch (MBeanException e) {
 // TODO Auto-generated catch block
 e.printStackTrace();
 } catch (ReflectionException e) {
 // TODO Auto-generated catch block
 e.printStackTrace();
 }
}

This works awesome in the same node where the service is running. But not in the others. It throws a javax.management.RuntimeMBeanException
.
Any ideas?