Low-cost flexible software fault tolerance for distributed computing

The authors revisit the problem of software fault tolerance in distributed systems. In particular, we propose an extension of a message-driven confidence-driven (MDCD) protocol we have developed for error containment and recovery in a particular type of distributed embedded system. More specifically, we augment the original MDCD protocol by introducing the method of "fine-grained confidence adjustment," which enables us to remove the architectural restrictions. The dynamic nature of the MDCD approach gives it a number of desirable characteristics. First, this approach does not impose any restrictions on interactions among application software components or require costly message-exchange based process coordination/synchronization. Second, the algorithms allow redundancies to be applied only to low-confidence or critical interacting software components in a distributed system, permitting flexible realization of software fault tolerance. Finally, the dynamic error containment and recovery mechanisms are transparent to the application and ready to be implemented by generic middleware.