Chapter 3. mod_cluster Connector

Create a Listen directive for the proxy server:

Edit your mod_cluster configuration file (usually JBCS_HOME/httpd/conf.d/mod_cluster.conf) to add the following:

Listen IP_ADDRESS:PORT_NUMBER

Where IP_ADDRESS is the address of the server network interface to communicate with the worker nodes, and PORT_NUMBER is the port on that interface to listen on.

Create a virtual host:

Add the following to your mod_cluster configuration file:

<VirtualHost IP_ADDRESS:PORT_NUMBER>

   <Directory />
      Require ip IP_ADDRESS
   </Directory>

   KeepAliveTimeout 60
   MaxKeepAliveRequests 0

   ManagerBalancerName mycluster
   AdvertiseFrequency 5
   EnableMCPMReceive On

</VirtualHost>

Where IP_ADDRESS and PORT_NUMBER are the values from the Listen directive.

Optional: Disable server advertisement:

The AdvertiseFrequency directive makes the server periodically send server advertisement messages via UDP multicast. By default, this occurs every 10 seconds.

These server advertisement messages contain the IP_ADDRESS and PORT_NUMBER specified in the VirtualHost definition. Worker nodes configured to respond to server advertisements use this information to register themselves with the proxy server.

To disable server advertisement, add the following directive to the VirtualHost definition:

ServerAdvertise Off

If server advertisements are disabled, or UDP multicast is not available on the network between the proxy server and the worker nodes, configure worker nodes with a static list of proxy servers.

Optional: Configure Apache HTTP Server Logging

You can configure the Apache HTTP Server that is doing the load balancing to log which worker node handled a request. This may be useful when troubleshooting your load balancer.

To enable this for mod_cluster, you can add the following to your Apache HTTP Server LogFormat directive(s):

For more information on Apache HTTP Server logging (including log rotation), see http://httpd.apache.org/docs/2.4/logs.html.

Stop and start the Apache HTTP Server service:

See the JBoss Core Services Installation Guide for detailed instructions.

Add a listener to Tomcat:

Add the following Listener element beneath the other Listener elements in JWS_HOME/tomcat<VERSION>/conf/server.xml.

<Listener className="org.jboss.modcluster.container.catalina.standalone.ModClusterListener" advertise="true" stickySession="true" stickySessionForce="false" stickySessionRemove="true" />

Give the worker a unique identity:

Edit JWS_HOME/tomcat<VERSION>/conf/server.xml and add the jvmRoute attribute and value to the Engine element, as shown below:

<Engine name="Catalina" defaultHost="localhost" jvmRoute="worker01">

Configure STATUS MCMP message frequency:

Tomcat worker nodes periodically send status messages containing their current load status to the Apache HTTP Server balancer. The default frequency of these messages is 10 seconds. If you have hundreds of worker nodes, the STATUS MCMP messages can increase traffic congestion on your Apache HTTP Server network.

You can configure the MCMP message frequency by modifying the org.jboss.modcluster.container.catalina.status-frequency Java system property. By default, the property accepts values in seconds*10. For example, setting the property to 1 means 10 seconds. The example below demonstrates setting the frequency to 60 seconds.

-Dorg.jboss.modcluster.container.catalina.status-frequency=6

Optional: Configure the firewall for proxy server advertisements:

A proxy server using mod_cluster can advertise itself via UDP multicast. Most operating system firewalls block this by default. To enable server advertising and receive these multicast messages, open port 23364 for UDP connections on the worker node’s firewall.

Define a mod_cluster Listener, and disable dynamic proxy discovery:

Edit JWS_HOME/tomcat<VERSION>/conf/server.xml , and add or change the Listener element for ModClusterListener. Set the advertise property to false. For example:

<Listener className="org.jboss.modcluster.container.catalina.standalone.ModClusterListener" advertise="false" stickySession="true" stickySessionForce="false" stickySessionRemove="true"/>

Create a static proxy server list:

Add a comma separated list of proxies to the Listener in the form of IP_ADDRESS:PORT as the proxyList property. For example:

<Listener className="org.jboss.modcluster.container.catalina.standalone.ModClusterListener" advertise="false" stickySession="true" stickySessionForce="false" stickySessionRemove="true" proxyList="10.33.144.3:6666,10.33.144.1:6666"/>