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Introduction

This article discusses how to install and configure Apache 2.0.x and Tomcat (or JBoss) to communicate with each other via mod_jk. This article also discusses how to setup a Tomcat cluster using mod_jk to balance work load.

Install JDK

1. Download JDK rpm and launch the executable by running the following commands:

   chmod a+x j2sdk-1_4_2_<version number>-linux-i586-rpm.bin
   ./j2sdk-1_4_2_<version number>-linux-i586-rpm.bin

2. Type yes and agree to the binary license agreement.
3. Become root by running su and entering root password
4. Install the rpm. This will install JDK at /usr/java/j2sdk-1.4.2:

   rpm -iv jdk-1.4.2_<version number>.i386.rpm

5. Edit PATH environment variable to include bin directory of JDK by adding the following lines to /etc/profile:

   JAVA_HOME=/usr/java/j2sdk-1.4.2_<version number>
   export JAVA_HOME
   PATH=$JAVA_HOME/bin:$PATH

Avoid Firewall and Routing issues

1. Disable the default firewall (unless you can configure it to allow multicast packets)

   /etc/init.d/iptables stop
   /etc/init.d/ip6tables stop

2. Add this multicast route:

   /sbin/route add -net 224.0.0.0 netmask 240.0.0.0 dev eth<id>

Install Apache

1. Download httpd-2.0.50-i686-pc-linux-gnu.tar.gz into a temporary location and run the following commands to install Apache at /usr/local/share:

   unzip < httpd-2.0.50-i686-pc-linux-gnu.tar.gz | tar xvf -
   cd httpd-2.0.50
   ./install-bindist.sh /usr/local/share/apache-2.0.50

2. Edit PATH environment variable to include bin directory of Apache by adding the following lines to /etc/profile:

   APACHE_HOME=/usr/local/share/apache-2.0.50
   export APACHE_HOME
   PATH=$APACHE_HOME/bin:$PATH
   export PATH

Install Tomcat

1. Move apache-tomcat-x.y.z.zip.zip to /usr/local/share (I will refer to the installation folder by this path) and unzip it:

   unzip apache-tomcat-x.y.z.zip

2. Edit PATH environment variable to include bin directory of Apache by adding the following lines to /etc/profile:

   TOMCAT_HOME=/usr/local/share/apache-tomcat-x.y.z
   export TOMCAT_HOME
   PATH=$TOMCAT_HOME/bin:$PATH
   export PATH

Configure mod_jk

1. Copy the mod_jk binary to $APACHE_HOME/modules directory and rename it as mod_jk.so
2. Add the following lines at the very bottom in $APACHE_HOME/conf/httpd.conf
   
   

   #Include mod_jk configuration file
   Include conf/mod-jk.conf

3. Under $APACHE_HOME/conf create mod-jk.conf and write the following lines in it:
   
   

   # Load mod_jk module
   # Specify the filename of the mod_jk lib
   LoadModule jk_module modules/mod_jk.so
   # Where to find workers.properties
   JkWorkersFile conf/workers.properties
   # Where to put jk logs
   JkLogFile logs/mod_jk.log
   # Set the jk log level [debug/error/info]
   JkLogLevel info
   # Select the log format
   JkLogStampFormat "[%a %b %d %H:%M:%S %Y]"
   # JkOptions indicates to send SSK KEY SIZE
   JkOptions +ForwardKeySize +ForwardURICompat -
   ForwardDirectories
   # JkRequestLogFormat
   JkRequestLogFormat "%w %V %T"
   JkMount /Context/* loadbalancer

   
   
   Where Context is the web-app context name.

4. Under $APACHE_HOME/conf create workers.properties and populate it as follows:
   
   

   # Worker list
   worker.list=loadbalancer
   # Define Node1
   worker.node1.port=8009
   worker.node1.host=node1.ip.address
   worker.node1.type=ajp13
   worker.node1.lbfactor=1
   #worker.node1.local_worker=1 (1)
   worker.node1.cachesize=10
   # Define Node2
   worker.node2.port=8009
   worker.node2.host=node2.ip.address
   worker.node2.type=ajp13
   worker.node2.lbfactor=1
   #worker.node2.local_worker=1 (1)
   worker.node2.cachesize=10
   # Load-balancer
   worker.loadbalancer.type=lb
   worker.loadbalancer.balanced_workers=node1, node2
   worker.loadbalancer.sticky_session=1
   worker.loadbalancer.local_worker_only=1

   Add one worker per node and name workers as node1, node2, node3 … nodeN. Don’t forget to define all these as load balancing workers:

   worker.loadbalancer.balanced_workers=node1, node2, node3, ... nodeN

   Replace node1.ip.address with IPAddress of Tomcat(or JBoss) instance1 and so on. The attribute sticky_session=1 tells mod_jk that SESSION ID’s should be routed back to the same Tomcat worker. The lbfactor determines the number of requests a worker receives. The higher the lbfactor the more requests a worker receives.

5. Each node should be named according to the names specified in workers.properties. On each Tomcat instance, edit $TOMCAT_HOME/conf/server.xml. Locate the <Engine> element and add an attribute called jvmRoute:

   <Engine name="Catalina" defaultHost="localhost" jvmRoute="node1">
   …
   </Engine>

NOTE: THE jvmRoute ATTRIBUTE MUST MATCH THE NAME SPECIFIED IN workers.properties.

Start Apache and Tomcat

1. Start Apache:

   $APACHE_HOME/bin/apachectl -k start

2. To stop use:

   $APACHE_HOME/bin/apachectl -k stop

3. Start Tomcat:

   $TOMCAT_HOME/bin/startup.sh

4. Stop Tomcat:

   $TOMCAT_HOME/bin/shutdown.sh