Yes - "Terracotta Sessions for Tomcat" works and is supported on RHEL v4. x
It is free for up to 4 client-nodes (you will have to get a license-key from Terracotta Sales before going into production). In terms of next steps, you could:
Simply download the Terracotta Enterprise Edition for RedHat: terracotta-2.0.0-rhel34-i686.tar.gz
Assuming you have downloaded Terracotta Sessions for Windows and have tested out session failover on your desktop - then you'd have a copy of the configuration file (tc-config.xml). Copy that config file over to the Terracotta home directory (that you downloaded in step 1) and use that.
If that config file is not available, then you will have to create the tc-config.xml file appropriately.
Note that you will have to modify your Tomcat startup scripts to enable DSO. (You could refer to the start-tomcat-9081.bat script that comes with the Windows build of Terracotta Sessions) and do what it does -- it just sets some environment variables.
The TomcatSRGuide.pdf in the docs directory under the install from (1) is a great resource, or you can always ask questions here.
Product Support Manager