I've spent a couple of weeks making my app "clusterable" w/ Terracotta. My goals are scalability and availability. Here are my initial impressions:
- Follows IoC paradigm. There is no API, so your code never becomes Terracotta dependent. Clustering is configured declaratively.
- Thread synchronization semantics are honored across the cluster. So, if your Threads are thread-safe, they can be clustered with no code changes (more ore less). Also, this allows powerful techniques for fail over and node death monitoring. I don't know if any other clustering libraries/frameworks with an equivalent feature.
- Integrated support for common problems: Hibernate, EHCACHE, session clustering.
- Error messages are descriptive and helpful, including solution suggestions
- Your app must be run with a special bootclasspath jar that must be created for the specific JRE you're using. This complicates deployment.
- Hub-and-spoke architecture - you have to run a separate Terracotta (TC) server application to which each cluster node will connect (which itself must be clustered to avoid a single point of failure). This also complicates deployment. Some (Tangersol Coherence guys) claim that this design also entails inherent performance limitations, which Terracotta disputes.
- All shared classes must be instrumented, which has the potential for causing problems in areas unrelated to clustering
- Configuration of locking can be tricky and difficult to debug