Virtual machine technology enables agile system deployments in which software components can be cheaply moved, replicated, and allocated hardware resources in a controlled fashion. This paper examines how these facilities can be used to provide enhanced solutions to the classic problem of ensuring high availability while maintaining performance. By regenerating software components to restore the redundancy of a system whenever failures occur, we achieve improved availability compared to a system with a fixed redundancy level. Moreover, by smartly controlling component placement and resource allocation using information about application control flow and performance predictions from queuing models, we ensure that the resulting performance degradation is minimized. We consider an environment in which a collection of multitier enterprise applications operates across multiple hosts, racks, clusters, and data centers to maximize failure independence. Simulation results show that our proposed approach provides better availability and significantly lower degradation of system response times compared to traditional approaches.
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