International Journal of Communication Networks and Distributed Systems
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Elastic compute clouds are best represented by the virtual clusters in Amazon EC2 or in IBM RC2. This paper proposes a simulation based approach to scheduling scientific workflows onto elastic clouds. Scheduling multitask workflows in virtual clusters is a NP-hard problem. Excessive simulations in months of time may be needed to produce the optimal schedule using Monte Carlo simulations. To reduce this scheduling overhead is necessary in real-time cloud computing. We present a new workflow scheduling method based on iterative ordinal optimization (IOO). This new method outperforms the Monte Carlo and Blind-Pick methods to yield higher performance against rapid workflow variations. For example, to execute 20,000 tasks on 128 virtual machines for gravitational wave analysis, an ordinal optimized schedule can be generated in a few minutes, which is O(103)~O(104) faster than using Monte Carlo simulations. The ordinal optimized schedule results in higher throughput with lower memory demand. The cloud experimental results being reported verified our theoretical findings on the relative performance of three workflow scheduling methods studied in this paper.