Enabling Technology for Fault Tolerance Ricardo Jiménez-Peris Marta Patiño-Martínez Technical University of Madrid (Universidad Politécnica de Madrid, UPM)

Enabling Technology for FT  Dependability is not as widespread as it should due to:  Common restrictions and assumptions that are not acceptable in realistic applications.  The high performance penalties of existing dependable solutions.  Lack of support or adequate interfaces in current middleware for providing FT.

Removing Restrictions for Applying FT  One of the common restriction to achieve FT has been the restriction of single-threaded servers.  Existing solutions for replicating multithreaded servers either restrict the potential concurrency or require an amount of inter-replica communication proportional the degree of synchronization.  An open-issue to be addressed is how to achieve FT of multithreaded servers, typical of current middleware platforms, with the above mentioned restrictions.  Another common restriction is the one of performing recovery and reconfiguration offline.  In order to provide high-available solutions is necessary to develop replication techniques in which recovery and reconfiguration can take place online.

Improving Performance of Fault-Tolerant Solutions  Existing approaches to fault-tolerance of stateful applications are either non-scalable or they sacrifice data consistency.  An important issue to be addressed is how to achieve scalable replication of stateful application whilst still guaranteeing full data consistency.  Another shortcoming usually associated to FT is that the latency of the resulting systems is too poor due to the cost of the underlying agreement protocols.  This is especially true when extending FT to WANs.  It should be addressed how this latency can be improved.

Middleware Support for FT e-Business  The ADAPT project addresses to some extent the FT support at middleware level.  The ADAPT partners are: Technical University of Madrid, Hewlett- Packard, Newcastle, Bologna, ETH Zurich, McGill, Trieste.  The project title is “Middleware Technologies for Adaptive and Composable Components”  The project deals with:  Adaptable web services.  Fault-tolerant and dynamically adaptable middleware (more specifically, J2EE-based application servers).  Workflow-like web service composition.  Predictable QoS of service compositions.  Service diversity for adaptable compositions.