Towards increasing reliability of clouds environments with RESTful web services

Recently, cloud computing has turned out to be a desired standard for development of distributed, large-scale applications. It allows to exploit on-demand various IT resources, ranging from virtual machines, storage, and databases to a broad set of cloud web services. Such services are closely intertwined with service-oriented architectures, and their design and implementation is often supported by Representational State Transfer methodology. Although cloud environments offering RESTful services constitute a desired computing model, their adoption is not free from challenges. Among the others, providing reliability of such environments poses difficulties and affects their usability. Since the simple restart of a failed processing (as a new instance) from the very beginning, is usually insufficient and often leads to unacceptable inconsistency of processing state, in this paper we propose a fault-tolerant mechanism that copes with this problem. In the proposed solution we introduce recovery consistency model that exploits semantics of REST operations and structure of resources, in order to flexibly determine formal requirements ensuring that the recovered processing state is compatible with REST constraints. Next, we put forward an efficient external upport of RESTful web services recovery, by presenting the protocol that extends ReServE rollback-recovery service and guarantees RESTful recovery consistency model. We provide a proof of protocol correctness, and experimentally evaluate efficiency of the proposed approach.