The cloud computing market has emerged as an alternative for the provisioning of resources on a pay-as-you-go basis. This flexibility potentially allows clients of cloud computing solutions to reduce the total cost of ownership of their Information Technology infrastructures. On the other hand, this market-based model is not the only way to reduce costs. Among other solutions proposed, peer-to-peer (P2P) grid computing has been suggested as a way to enable a simpler economy for the trading of idle resources. In this paper, we consider an IT infrastructure which benefits from both of these strategies. In such a hybrid infrastructure, computing power can be obtained from in-house dedicated resources, from resources acquired from cloud computing providers, and from resources received as donations from a P2P grid. We take a business-driven approach to the problem and try to maximise the profit that can be achieved by running applications in this hybrid infrastructure. The execution of applications yields utility, while costs may be incurred when resources are used to run the applications, or even when they sit idle. We assume that resources made available from cloud computing providers can be either reserved in advance, or bought on-demand. We study the impact that long-term contracts established with the cloud computing providers have on the profit achieved. Anticipating the optimal contracts is not possible due to the many uncertainties in the system, which stem from the prediction error on the workload demand, the lack of guarantees on the quality of service of the P2P grid, and fluctuations in the future prices of on-demand resources. However, we show that the judicious planning of long term contracts can lead to profits close to those given by an optimal contract set. In particular, we model the planning problem as an optimisation problem and show that the planning performed by solving this optimization problem is robust to the inherent uncertainties of the system, producing profits that for some scenarios can be more than double those achieved by following some common rule-of-thumb approaches to choosing reservation contracts.
['Paulo Ditarso Maciel', 'Francisco Vilar Brasileiro', 'Raquel Vigolvino Lopes', 'Marcus Carvalho', 'Miranda Mowbray']
Evaluating the impact of planning long-term contracts on the management of a hybrid IT infrastructure