Energy Aware Resource Management for Clusters of Web Servers

Web server clusters guarantee high performance and high availability for applications like google and amazon. Typically, over-provisioning is used to guarantee a Service Level Agreement in the case of peak load situations. We present an energy saving mechanism which extends the capabilities of traditional load balancers like for example the Linux Virtual Server (LVS). The energy saving daemon called Cherub, running on the front node of the cluster, turns nodes on and off depending on the current load situation. We evaluate different load determination and forecasting methods to detect the utilization of the back end servers in a test bed using requests from a web server log file of the Wikimedia Foundation. Even for the most challenging situation, i.e. in case of a peak load, LVS enhanced with Cherub saves 92% of the theoretical possible optimum saving, while keeping the service level agreement at 99.4% in the experiment.