Cloud computing enables the dynamic provisioning of server resources. To exploit this opportunity, a policy is needed for dynamically allocating (and deallocating) servers in response to the current load conditions. In this paper we describe several simple policies for dynamic server allocation and develop analytic models for their analysis. We also design semi-Markov decision models that enable determination of the performance achieved with optimal policies, allowing us to quantify the performance gap between simple, easily implemented policies, and optimal policies. Finally, we apply our models to study the potential performance benefits of state-dependent routing in multi-site systems when using dynamic server allocation at each site. Insights from our results are valuable to service providers wanting to balance cloud service costs and delays.

翻译：云计算能够实现服务器资源的动态配置。为充分利用这一特性，需要制定根据当前负载条件动态分配（及释放）服务器的策略。本文描述了若干种简单的动态服务器分配策略，并建立了分析模型对其进行评估。同时，我们设计了半马尔可夫决策模型，能够确定最优策略下的性能表现，从而量化简单易实现的策略与最优策略之间的性能差距。最后，我们将模型应用于研究多站点系统中，各站点采用动态服务器分配时，状态相关路由的潜在性能优势。研究结果对于希望平衡云服务成本与延迟的服务提供商具有重要参考价值。