Web server cluster has been widely used to improve the performance and reliability of web servers. Web cluster is usually deployed to handle peak load, resulting in an excessive waste of energy; hence, its deployment should be dynamically adjusted according to real-time load demand. This paper proposes an online automatic energy-efficient deployment scheme for web cluster, which tries to minimize cluster's energy consumption under QoS guarantee. The scheme uses both CPU dynamic frequency scaling and server dynamic switching on/off mechanisms to reduce power consumption. It uses M/G/1 PS queue model to model server, and transforms cluster's deployment problem to a constrained programming problem. Moreover, a hybrid algorithm is proposed to solve the problem. The algorithm adopts greedy idea to determine the on/off state of each server and adopts chaotic optimization to search the optimal solution. Due to the fewer variables and efficient solving algorithm, the problem can be solved online even applied in large-scale clusters. Simulation tests demonstrate that the hybrid solving algorithm can find high-quality solution in less computing time.

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