Modelling exogenous variability in cloud deployments

  • Authors:
  • Giuliano Casale;Mirco Tribastone

  • Affiliations:
  • Imperial College London, London, United Kingdom;Ludwig-Maximilians-Universität, Munich, Germany

  • Venue:
  • ACM SIGMETRICS Performance Evaluation Review
  • Year:
  • 2013

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Abstract

Describing exogenous variability in the resources used by a cloud application leads to stochastic performance models that are difficult to solve. In this paper, we describe the blending algorithm, a novel approximation for queueing network models immersed in a random environment. Random environments are Markov chain-based descriptions of timevarying operational conditions that evolve independently of the system state, therefore they are natural descriptors for exogenous variability in a cloud deployment. The algorithm adopts the principle of solving a separate transient-analysis subproblem for each state of the random environment. Each subproblem is then approximated by a system of ordinary differential equations formulated according to a fluid limit theorem, making the approach scalable and computationally inexpensive. A validation study on several hundred models shows that blending can save up to two orders of magnitude of computational time compared to simulation, enabling efficient exploration of a decision space, which is useful in particular at design-time.