To setup httpd with mod_cluster, refer to the mod_cluster docs:

http://docs.jboss.org/mod_cluster/1.2.0/html/

I encourage you to also configure httpd w/mod_advertise.  This way, you do not need to configure anything within AS7 itself.  When using mod_advertise, your httpd instance will announce itself to your AS7 nodes.

To enable session replication, simply add <distributable/> to your web.xml.  Once your application is deployed, the AS will automatically register your application with mod_cluster, and httpd will start directing traffic to your node.  To customize load balancing behavior, refer again to the mod_cluster docs.

Oops - I didn't notice your post title, indicating that you're running on EC2.

In that case, you'll need to make the following modifications:

1. You cannot use mod_advertise, since multicast will not work.  Remove the mod_advertise module entirely, and set advertise="false" within the mod_cluster subsystem in AS7.

2. Define the location of your httpd instance using the "proxy-list" attribute in the mod_cluster subsystem.

3. Change the default-stack of the jgroups subsystem to "tcp" instead of "udp".

4. Replace MPING with S3_PING within the "tcp" stack.