Architectural Support for Dynamic Reconfiguration of Large Scale Distributed211 Applications

摘要

In a distributed environment, it is inevitable that long running applications211u001ewill require support for dynamic reconfiguration because, for example, machines 211u001emay fail, services may be moved or withdrawn and user requirements may change. In 211u001esuch an environment it is essential that the structure of running applications 211u001ecan be modified to reflect such changes. A compliation is that such long running 211u001eapplications are frequently composed out of existing applications. The resulting 211u001eapplication can be very complex in structure, containing many temporal 211u001edependencies between constituent applications. This paper describes an approach 211u001ethat supports the dynamic reconfiguration of large scale distributed 211u001eapplications. An application composition and execution environment has been 211u001edesigned and implemented as a transactional workflow system that enables sets of 211u001einter-related tasks (applications) to be carried out and supervised in a 211u001edependable manner. A task model that is expressive enough to represent temporal 211u001edependencies between constituent tasks has been developed. The workflow system 211u001emaintains this structure and makes it available through transactional operations 211u001efor performing changes to it. Use of transactions ensure that changes can be 211u001ecarried out atomically with respect running applications. The workflow system is 211u001egeneral purpose and open: it has been designed and implemented as a set of CORBA 211u001eservices to run on top of a given ORB.