A Cluster-Based Web System Providing Differentiated and Guaranteed Services

  • Authors:

  • Mauro Andreolini;Emiliano Casalicchio;Michele Colajanni;Marco Mambelli

  • Affiliations:

  • University of Roma Tor Vergata, Roma, Italy 00133;University of Roma Tor Vergata, Roma, Italy 00133;University of Modena, Modena, Italy 41100;University of Modena, Modena, Italy 41100

  • Venue:
  • Cluster Computing
  • Year:
  • 2004

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Abstract

In a world where many users rely on the Web for up-to-date personal and business information and transactions, it is fundamental to build Web systems that allow service providers to differentiate user expectations with multi-class Service Level Agreements (SLAs). In this paper we focus on the server components of the Web, by implementing QoS principles in a Web-server cluster that is, an architecture composed by multiple servers and one front-end node called Web switch. We first propose a methodology to determine a set of confident SLAs in a real Web cluster for multiple classes of users and services. We then decide to implement at the Web switch level all mechanisms that transform a best-effort Web cluster into a QoS-enhanced system. We also compare three QoS-aware policies through experimental results in a real test-bed system. We show that the policy implementing all QoS principles allows a Web content provider to guarantee the contractual SLA targets also in severe load conditions. Other algorithms lacking some QoS principles cannot be used for respecting SLA constraints although they provide acceptable performance for some load and system conditions.