What is Hedera?

Hedera is an open-source framework designed to provide a uniform API to different group communication libraries. The currently available instance sits on top of JGroups and Appia. It is also available a preliminary implementation that uses Spread. Hedera is the continuation of the Tribe project.

Hedera is targeted at reliable group communication within clusters. In such environments, we expect group memberships to be relatively stable and group sizes to be moderate (at most a few hundreds). However, we expect a potentially large number of logical groups.

In the framework of the Sequoia technology, group communication is needed to support replicated databases where the replicas are managed by different controllers.

For an overview of some of the concepts related to Hedera, look at Distributed Systems Concepts and Design by G. Couloris, J. Dollimore and T.Kindberg, 2001. In particular section 11.4 about multicast communication and section 14.2 about group communication.