This week's book giveaways are in the Refactoring and Agile forums. We're giving away four copies each of Re-engineering Legacy Software and Docker in Action and have the authors on-line! See this thread and this one for details.
Tomcat using Session Persistence to help retreive a session after it shutdowns or crashes. It's also used within clustered environments. I think that it's enabled by default, but uou can disable it. I don't think that it's part of the specification (except the part on distributed environments).