Session replication only functions for Enterprise Licenses. The servers participating in the replication must have a manual setting configuration done in their prefs.xml file.
Edit the prefs.xml file and fill in the entry for: replicate_session_host_port
Example for the first machine:
<replicate_session_host_port>192.168.1.19:7800</replicate_session_host_port>
and on the second machine a reference back to the first machine.
<replicate_session_host_port>192.168.1.18:7800</replicate_session_host_port>
To enable user replication from changes made in the user manager, edit the prefs.xml file and set this flag to true.
<replicated_users_sync>true</replicated_users_sync>
In some special cases you may want the other functionality without the overhead of all session information being replicated between machines. In this case a user would have to re-login if they were suddenly redirected to the other machine...but it avoid wasted resources from replicating all details about a user between machines. Set this to false.
<replicate_sessions>false</replicate_sessions>