java concurrency web application + clustering

HttpSession
Sticky session

[main]
Modern concurrency and Java EE
http://java.dzone.com/articles/modern-concurrency-and-java-ee

Java theory and practice: Are all stateful Web applications broken?
http://www.ibm.com/developerworks/library/j-jtp09238/

Java theory and practice: State replication in the Web tier
http://www.ibm.com/developerworks/java/library/j-jtp07294/index.html