IdP clustering without Terracotta?

[Joel Goguen]

I've got an IdP server set up right now with CAS and Shibboleth IdP sharing a Tomcat instance. The IdP delegates authentication to CAS (per https://wiki.jasig.org/display/CASUM/Shibboleth-CAS+Integration under "Designate CAS the Authentication Provider for Shib IDP"). Accordingly, Shibboleth only uses RemoteUser authentication, and I've also removed the PreviousSession LoginHandler. The server is CentOS 6 x64, running Tomcat 6 fronted by Apache and mod_proxy_ajp 

What I need to do now is cluster this service in some manner compatible with Java 7 (so no Terracotta) and  the following:
- A server must be able to be removed manually from the cluster without service interruption
- A server which goes down must be automatically removed from the cluster quickly
- It would be preferable if the downed node could be automatically re-added to the cluster once it's available again
- Users must not notice if they get bounced between cluster members - it must appear to be a single service from the end-user's perspective. 

So... how far out in left field am I? Or is there something that could work well for me?

-- 
Joel Goguen
Developer
Enterprise Solutions
Information Technology Services
University of New Brunswick
Email: joel.goguen at unb.ca
Phone: (506) 453-4872
Fax: (506) 453-3590