Consensus service: a modular approach for building agreement protocols in distributed systems

We describe a consensus service and suggest its use for the construction of fault-tolerant agreement protocols. We show how to build agreement protocols, using a classical client-server interaction, where: the clients are the processes that must solve the agreement problem; and the servers implement the consensus service. Using a generic notion, called consensus filter, we illustrate our approach on non-blocking atomic commitment and on view synchronous multicast. The approach can trivially be used for total order broadcast. In addition of its modularity, our approach enables efficient implementations of the protocols, and precise characterization of their liveness.