An approach for fault-tolerance in hard real-time distributed systems

The presence of hard timing constraints makes the design of fault tolerant systems difficult because when tasks are replicated to treat errors, both the task replicas and the fault tolerance building blocks (e.g., consensus) must be taken into account in the feasibility tests. This paper is devoted to the description of an approach for managing failures in hard real time distributed systems. Our approach is based on the use of a task replication tool named Hydra which makes tasks fault-tolerant off-line through the replication of parts to their code. The contribution of our work is not to provide new replication strategies but rather to provide replication strategies that are simultaneously suited to real time constraints, transparent to application designers and flexible (i.e., adaptable to application requirements and with low dependence with the underlying run-time support and hardware). Further details on Hydra can be found in (Chevochot and Puaut, 1999).