3.2. Configure Load Balancing Using Apache HTTP Server and mod_cluster

Procedure 3.1. Configure a Load-balancing Proxy Using mod_cluster

1. Create a Listen Directive for the Proxy Server

   Edit your mod_cluster configuration file (usually JWS_HOME/httpd/conf.d/mod_cluster.conf), and 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.

   Note

   The port must be open for incoming TCP connections.

   Example 3.1. Example Listen Directive

   Listen 10.33.144.3:6666

2. 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.

3. Optional: Disable Server Advertisement

   The AdvertiseFrequency directive makes the server to periodically send server advertisement messages via UDP multicast. By default, this occurs every 5 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. See Section 3.2.2.2, “Configuring a Worker Node with a Static Proxy List”.

4. 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):

   %{BALANCER_NAME}e

   The name of the balancer that served the request.

   %{BALANCER_WORKER_NAME}e

   The name of the worker node that served the request.

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

5. Stop and Start the JBoss Web Server Apache Service

   See the JBoss Web Server Installation Guide for detailed instructions.

Procedure 3.2. Configure a Tomcat Worker Node

1. 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" />

2. 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">

3. 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 property. By default, the property accepts values in seconds*10. For example, setting the property to 1 means 10 seconds. The example below demonstrates the frequency set to 60 seconds.

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

4. Optional Step: Configure 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.

   • For Red Hat Enterprise Linux 6

     /sbin/iptables -A INPUT -m state --state NEW -m udp -p udp --dport
      23364 -j ACCEPT 
     -m comment -comment "receive mod_cluster proxy server advertisements"

     If Automatic Proxy Discovery is not used, configure worker nodes with a static list of proxies. In this case you can safely ignore the following warning message:

     [warning] mod_advertise: ServerAdvertise Address or Port not defined, Advertise disabled!!!

   • For Red Hat Enterprise Linux 7

     firewall-cmd --permanent --zone=public --add-port=23364/udp

   • For Microsoft Windows, using PowerShell

     Start-Process "$psHome\powershell.exe" -Verb Runas -ArgumentList '-command "NetSh Advfirewall firewall add rule name="UDP Port 23364" dir=in  action=allow protocol=UDP localport=23364"'
     Start-Process "$psHome\powershell.exe" -Verb Runas -ArgumentList '-command "NetSh Advfirewall firewall add rule name="UDP Port 23364" dir=out action=allow protocol=UDP localport=23364"'

Procedure 3.3. Configure JBoss Web Server Worker Node with a Static Proxy List

1. Define a mod_cluster listener, and Disable Dynamic Proxy Discovery

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

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

2. Create a static proxy server list

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

   Example 3.2. Example Static Proxy List

   <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"/>