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JBoss Interview Questions and Answers

Ques 1. What is JBoss?

JBoss is a popular open source application server based on Java EE technology. Being Java EE based, the JBoss supports cross-platform java applications. It was embedded with Apache Tomcat web server. It runs under any JVM of 1.3 or later versions. JBoss supports JNDI, Servlet/JSP (Tomcat or Jetty), EJB, JTS/JTA, JCA, JMS, Clustering (JavaGroups), Web Services (Axis), and IIOP integration (JacORB).

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Ques 2. How to build clusters in JBoss?

Here is a nutshell summary from the example given for quick start: 
Execute from your jboss bin directory:
$ ./run.sh -c all -g DocsPartition -u 239.255.100.100 -b 192.168.0.101 -Djboss.messaging.ServerPeerID=1

  • ./run.sh = the executable
  • -c all = use server in jboss_home/server/all directory
  • -g DocsPartition = this is the partition name, use whatever but should be the same across nodes
  • -u 239.255.100.100 = this is the multicast address, ususally just pick anything in the 239.255.x.y range and you should be ok
  • -b 192.168.0.101 = this is the ip of the machine the node is on
  • -Djboss.messaging.ServerPeerID=1 = this is the peerid, it must be unique for each node.
So the start script that you would run on your second machine for the second node would look like:
$ ./run.sh -c all-node2 -g DocsPartition -u 239.255.100.100 -b 192.168.0.102 -Djboss.messaging.ServerPeerID=2
You can also use nohup to send the process to the background.
Now that both nodes should be running, you have to enable and configure the sticky sessions on the webserver and each server.

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Ques 3. How do you monitor JBoss and detect the bottleneck of an application?

The first step is to measure the different components of your app to see where the degradation is. Is it an external resource (database, message server, etc.) or internal? Where is the app spending all its time?

So the first step could be to use JBoss JMX agents and monitor the components deployed to the application server. Once it's clear which component or library takes most of the time or most of resource you can use a more specialized tool like JProbe and examine the single method or the single objects loaded in memory.

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Ques 4. What's JBoss cache in short?

JBossCache enables easy distribution of datasets across your computing environments. It is based on JGroups and enables clustering and high availability of that data. You may choose to distribute the data with JBoss Messaging to move it where it is needed for computation or event-based programming.

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Ques 5. What are needed to set-up a cluster with JBoss?

Basically starting JBoss with the 'all' configuration contains everything needed for clustering:

It has all the libraries for clustering:

  • JGroups.jar, jboss-cache.jar
  • Clustered beans (cluster-service.xml)
  • HA-JNDI
  • HTTP session replications (tc5-cluster-service.xml)
  • Farming
  • HA-JMS

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