Terracotta releases free 4 node Tomcat Session Clustering
The products can thus be used to provide distributed clustering and high availability of HTTPSessions on web farms, but even in situations where sticky-load balancers are in use and no data is being shared, Terracotta sessions can be used to have the 'hub' keep a backup of all data on each node and transparently fail over to another server should one machine go down.
Terracotta's other main product is DSO (Distributed Shared Objects), which is a VM clustering software aimed at transparently clustering any object in the VM without any code changes (such as serialization). DSO slots itself in at the heap layer, replicating changes from one heap to heaps in other VM's that need that change. DSO also coordinates sychronization between threads, and can migrate threads across server instances. Currently in the research labs, they are also working on a mechanism to cluster threads, so that a thread pool could also be clustered across machines.
Doc List Oct 25, 2014