Enhancing a web-server cluster with quality of service mechanisms

We introduce the concept of "quality of web-based services" (QoWS) which is inspired by the well known QoS principles for networks, but it is focused on the server side of the web system. In particular, we investigate how it is possible to enhance with QoWS mechanisms a web site that is hosted on a system platform consisting of locally distributed server nodes, namely web-server cluster or web cluster in short. We discuss and compare some QoWS policies and mechanisms that can be used to transform a best-effort web cluster into a QoWS-enhanced system. We determine a set of confident Service Level Agreements (SLAB) in a web cluster for different classes of users and web services. Moreover; we verify through a large set of simulation experiments under realistic workload models which mechanisms are valid for satisfying the pre-determined SLA target.