Clustering with JBoss mod_cluster

Mod cluster is an http based load balancer which greatly simplify the setup of an http cluster. It ships as a set of modules which need to be installed on the httpd server and a Service Archive Library (.sar) which needs to be deployed on WildFly.

Wildfly is also able to handle front-end requests with the load-balancer profile. Check this tutorial to learn more: Configuring High Availability with WildFly

Compared with the former mod_jk, the new mod_cluster has the great advantage to accept a dynamic configuration of httpd workers. This can be done through an advertise mechanism where all httpd workers communicate lifecycle events (like startup or shutdown) thus leveraging dynamic configuration of nodes.

 

The following picture describes an high level view of the communication between the httpd server and a set of JBoss nodes:

As you can see, mod_cluster issues requests to mod_proxy_ajp which forwards the AJP request to the target node of the cluster. The cluster of JBoss nodes communicates the cluster view to mod_cluster.

The installation of mod_cluster is slightly different depending on the release of the application server. If you are running JBoss AS 5.1.0 you need to execute all the steps listed in this tutorial. If you are running JBoss AS 6 or 7 you need just to execute steps 2 (Install Binaries) and 4 (Update Apache configuration).

At first move to the Download page and download the following items:

 

1) Download the Java Bundle package which contains the Service Archive (.sar) to be deployed on JBoss
2) Download the binaries for your platform which contains a built-in httpd server and its modules (including mod_cluster).

1. Installing Java Bundles

From the bundle tar.gz, copy the file mod-cluster.sar in the “deploy/cluster”  folder of your “all” configuration:

The modules can be extracted from the archive mod-cluster-1.0.3.GA-xxx-ssl.zip. The modules need to be copied in the APACHE_HOME/modules dir.

 

Now open the file server.xml which contains the embedded Web Server configuration and is located in the deploy/jbossweb.sar/ folder and add the following line at the same level of other Listeners:

<Listener className="org.jboss.web.tomcat.service.deployers.MicrocontainerIntegrationLifecycleListener"            delegateBeanName="ModClusterService"/>

In the same file, a few lines after, add the jvmRoute in the Engine element:

<Engine name="jboss.web" defaultHost="localhost"  jvmRoute="node01"> 

Next file we need to modify is jboss-beans.xml which is located in the deploy/jbossweb.sar/META-INF folder. There we need to state that the WebServer depends on the Mod Cluster Service.

Just add the following dependency to the WebServer bean (approx line 16)

 <depends>ModClusterService</depends> 

Provided that you have copied all modules in the previous step, all you have to do is loading the modules in the httpd memory and configure a VirtualHost for handling requests to JBoss cluster.

In order to enable mod_cluster, the following modules need to be enabled:

LoadModule proxy_module /modules/mod_proxy.so
LoadModule proxy_ajp_module /modules/mod_proxy_ajp.so
LoadModule slotmem_module /modules/mod_slotmem.so
LoadModule manager_module /modules/mod_manager.so
LoadModule proxy_cluster_module /modules/mod_proxy_cluster.so
LoadModule advertise_module /modules/mod_advertise.so

Then, add this configuration to the bottom of your Apache’s httpd.conf file:

Listen 192.168.1.0:6666

<VirtualHost 192.168.1.0:6666>   
    <Directory />     
       Order deny,allow     
       Deny from all     
       Allow from 192.168.1.  
   </Directory> 

   KeepAliveTimeout 60
   MaxKeepAliveRequests 0  
   ManagerBalancerName mycluster
   AdvertiseFrequency 5 
</VirtualHost>

Here we assume that your Apache listen to the IP Address 192.168.1.0 and accepts requests on port 6666.

run.sh -c all -b 192.168.1.10

standalone.sh -c standalone-ha.xml -b 192.168.1.10