Here is a simple straight forward install instruction for the glassfish loadbalancer plugin on linux apache. Notice that this plugin is only available for glassfish 2.x and works only with 32bit apache. All the steps must be run as the root user.

Install the required packages, and enable them:

yum install httpd.i386 mod_ssl.i386 -y
chkconfig httpd on

Download and unzip the glassfish plugin:

cd ~
mkdir glassfish
cd glassfish
wget http://dlc.sun.com.edgesuite.net/javaee5/external/Linux/aslb/jars/aslb-9.1.1-b17.jar
unzip aslb-9.1.1-b17.jar
unzip SUNWaslb.zip
unzip SUNWaspx.zip

Create the appropriate directories:

mkdir /etc/httpd/modules/resource
mkdir /etc/httpd/modules/errorpages
mkdir /etc/httpd/sec_db_files

Next, put all the unzip files on the right location:

cp ~/glassfish/lib/webserver-plugin/linux/apache2.2/LBPlugin*.res /etc/httpd/modules/resource -f
cp ~/glassfish/lib/webserver-plugin/linux/apache2.2/mod_loadbalancer.so /etc/httpd/modules
cp ~/glassfish/lib/webserver-plugin/linux/apache2.2/errorpages/* /etc/httpd/modules/errorpages/
cp ~/glassfish/lib/dtds/sun-loadbalancer* /etc/httpd/conf/
cp ~/glassfish/lib/install/templates/loadbalancer.xml.example /etc/httpd/conf
cp ~/glassfish/lib/webserver-plugin/linux/apache2.2/*.db /etc/httpd/sec_db_files/
cp ~/glassfish/lib/lib* /usr/lib

Enable the plugin:

cat >> /etc/httpd/conf/httpd.conf << EOF
##BEGIN EE LB Plugin Parameters
LoadModule apachelbplugin_module modules/mod_loadbalancer.so

config-file "/etc/httpd/conf/loadbalancer.xml"
locale en


DocumentRoot "/var/www/html"
ServerName [SERVERNAME]

Next, configure the loadbalancer:

vi /etc/httpd/conf/loadbalancer.xml

Remember to add an entry for every context root of your application in the loadbalancer.xml, other wise this part of the application will not be available through the loadbalancer.

Enable and configure apache as a worker:

vi /etc/httpd/conf/httpd.conf

Set the following parameters:

StartServers 1
MaxClients 32
MinSpareThreads 5
MaxSpareThreads 10
ThreadsPerChild 32
MaxRequestsPerChild 0

Enable worker processes:

vi /etc/sysconfig/httpd

HTTPD=/usr/sbin/httpd.worker

Pro’s: this way of balancing your J2EE application, the loadbalancer is aware that he is balancing a java application. Mod_proxy is not.
Con’s: Pretty maintenance intensive, every context root must be added to the configuration.