Designing fault-tolerant SOA based on design diversity.

Background: Over recent years, software developers have been evaluating the benefits of both Service-Oriented Architecture (SOA) and software fault tolerance techniques based on design diversity. This is achieved by creating fault-tolerant composite services that leverage functionally-equivalent services. Three major design issues need to be considered while building software fault-tolerant architectures based on design diversity: (i) selection of variants; (ii) selection of an adjudication algorithm to choose one of the results; and (iii) execution of variants. In addition, applications based on SOA need to function effectively in a dynamic environment where it is necessary to postpone decisions until runtime. In this scenario, control is highly distributed and involves conflicting user requirements. We aim to support the software architect in the design of fault-tolerant compositions. Methods: Leveraging a taxonomy for fault-tolerant systems, this paper proposes guidelines to aid software architects in making key design decisions. The taxonomy is used as the basis for defining a set of guidelines to support the architect in making decisions related to fault tolerance in SOA. The same taxonomy is used in a systematic literature review of solutions for fault-tolerant composite services. The review investigates how existing approaches for fault-tolerant composite services address design diversity issues and also specific issues related to SOA. Results: The contribution of this work is twofold: (i) a set of guidelines for supporting the design of fault-tolerant SOA, based on a taxonomy for fault tolerance techniques; and (ii) a systematic literature review of existing solutions for designing fault-tolerant compositions using design diversity. Conclusion: Although existing solutions have made significant contributions to the development of fault-tolerant SOAs, there is a lack of approaches for fault-tolerant service composition that support strategies with diverse quality requirements and encompassing sophisticated context-aware capabilities. This paper discusses which design issues have been addressed by existing diversity-based approaches for fault-tolerant composite services. Finally, practical issues and difficulties are summarized and directions for future work are suggested