Web sites are exposed to high rates of incoming requests. The servers may become overloaded during temporary traffic peaks when more requests arrive than the server is designed for. An admission control mechanism rejects some requests whenever the arriving traffic is too high and thereby maintains an acceptable load in the system. This paper presents how admission control mechanisms can be designed with a combination of queueing theory and control theory. In this paper we model an Apache web server as a GI/G/1-system and then design a PI-controller, commonly used in automatic control, for the server. The controller has been implemented as a module inside the Apache source code. Measurements from the laboratory setup show how robust the implemented controller is, and how it corresponds to the results from the theoretical analysis.
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机译：网站面临大量传入请求。当到达的请求数量超出服务器的预期数量时，在临时流量高峰期间，服务器可能会变得过载。只要到达的流量过高，准入控制机制就会拒绝某些请求，从而在系统中维持可接受的负载。本文介绍了如何结合排队论和控制理论来设计准入控制机制。在本文中，我们将Apache Web服务器建模为GI / G / 1系统，然后为该服务器设计通常用于自动控制的PI控制器。该控制器已实现为Apache源代码内部的模块。实验室设置的测量结果显示了所实施控制器的坚固程度，以及其与理论分析结果的对应关系。
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