Supporting Dependable Distributed Applications Through a Component-Oriented Middleware-Based Group Service

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Dependable distributed applications require flexible infrastructure support for controlled redundancy, replication, and recovery of components and services. However, most group-based middleware platforms, which are increasingly being used as implementation environments for such systems, fail to provide adequate flexibility to meet diverse application requirements. This paper presents a group-based middleware platform that aims at maximal flexibility. In particular, flexibility is provided at design time, deployment time and run-time. At design and deployment time, the developer can configure a system by assembling software components shaped to a specific use. Then, at run-time, s/he can dynamically reconfigure the resulting system to adjust it to new circumstances, or can add arbitrary machinery to enable the system to perform self-adaptation. As examples, levels of fault tolerance can be dynamically increased and decreased as desired by adding, removing or replacing replicas; or the underlying communications topology can be adapted by switching from point-to-point TCP to multicast as numbers of replicants increase. Importantly, it is not necessary that the shape that run-time reconfiguration takes has been foreseen at design or deployment time. Our proposed solution employs software component technology and computational reflection as the basic means by which to perform and manage configuration and reconfiguration.