Three-tier replication for FT-CORBA infrastructures

摘要

Enforcing strong replica consistency among a set of replicas of a service deployed across an asynchronous distributed system in the presence of crash failures is a real practical challenge. If each replica runs the consistency protocol bundled with the actual service implementation, this target cannot be achieved, as replicas need to be located over a partially synchronous distributed system to solve the distributed agreement problems underlying strong replica consistency. A three-tier architecture for software replication enables the separation of the replication logic, i.e. protocols and mechanisms necessary for managing software replication, from both clients and server replicas. The replication logic is embedded in a middle-tier that confines the need of partial synchrony and thus frees replica deployment. In this paper we first introduce the basic concepts underlying three-tier replication. Then we present the interoperable replication logic (IRL) architecture, a fault-tolerant CORBA compliant infrastructure. IRL exploits a three-tier approach to replicate stateful deterministic CORBA objects and allows object replicas to run on object request brokers from different vendors. A description of an IRL prototype developed in our department is proposed along with an extensive performance analysis.