text: Infrastructure as a service clouds hide the complexity of maintaining the physical infrastructure with a slight disadvantage: they also hide their internal working details. Should users need knowledge about these details e.g., to increase the reliability or performance of their applications, they would need solutions to detect behavioural changes in the underlying system. Existing runtime solutions for such purposes offer limited capabilities as they are mostly restricted to revealing weekly or yearly behavioural periodicity in the infrastructure. This article proposes a technique for predicting generic background workload by means of simulations that are capable of providing additional knowledge of the underlying private cloud systems in order to support activities like cloud orchestration or workflow enactment. Our technique uses long-running scientific workflows and their behaviour discrepancies and tries to replicate these in a simulated cloud with known (trace-based) workloads. We argue that the better we can mimic the current discrepancies the better we can tell expected workloads in the near future on the real life cloud. We evaluated the proposed prediction approach with a biochemical application on both real and simulated cloud infrastructures. The proposed algorithm has shown to produce significantly ( 20 ) better workload predictions for the future of simulated clouds than random workload selection.
  @cite_11: Execution of workflow applications in Cloud environments involves many uncertainties because of elastic resource provisioning and unstable performance of multitenant virtual machines (VM) instances over time. These uncertainties are usually either neglected by existing researches, or modeled with some probability distribution function. To address this gap, we extend a multi-objective workflow scheduling algorithm (MOHEFT) in two directions: (1) to deal with the dynamic nature of Cloud environments offering a potentially infinite amount of on-demand resources, and (2) to consider robustness as an objective that mitigates the variability in VM performance over time. Our new robust model, called R-MOHEFT, considers uncertainty in processing times of workflow activities without a precise estimation or known distribution function within an uncertainty interval. We approach this scheduling problem as a three-objective optimisation that considers makespan, monetary cost, and robustness as simultaneous objectives of a commercial Cloud environment. Our new algorithm is able to estimate the Pareto optimal set of scheduling solutions that resist against fluctuations in processing times three times better than its MOHEFT predecessor, with a tradeoff of only 15 worse Pareto frontier. R-MOHEFT's hypervolume suffers by only 5 to 16 , compared to the MOHEFT's drawback of 38 to surprisingly 87 , when the processing time fluctuates up to its double value.
summary: @cite_11 also identified performance uncertainties of multi-tenant virtual machine instances over time in Cloud environments. They proposed a model called R-MOHEFT that considered uncertainty intervals for workflow activity processing times. They developed a three-objective (i.e., makespan, monetary cost, and robustness) optimisation for Cloud scheduling in a commercial setting. In contrast to this approach our goal is to identify patterns in earlier workloads to overcome the uncertainty, and apply simulations to predict future background load of the infrastructure.