Application-transparent fault tolerance in distributed systems

We present a new software architecture in which all concepts necessary to achieve fault tolerance can be added to an application automatically without any source code changes. As a case study, we consider the problem of providing a reliable service despite node failures by executing a group of replicated servers. Replica creation and management as well as failure detection and recovery are performed automatically by a separate fault tolerance layer (ft-layer) which is inserted between the server application and the operating system kernel. The layer is invisible for the application since it provides the same functional interface as the operating system kernel, thus making the fault tolerance property of the service completely transparent for the application. A major advantage of our architecture is that the layer encapsulates both fault tolerance mechanisms and policies. This allows for maximum flexibility in the choice of appropriate methods for fault tolerance without any changes in the application code