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The future will see more and more cloud service providers joining forces as cloud federations so as to offer their customers a wider range of services whilst optimizing usage of their resources. Service level agreements (SLAs) form the basis for these federations by defining the quality of services between the providers themselves and between the provider and the customer. The distributed, SLA-based scheduling of virtual machines (VMs) presents a major challenge. For this reason a general model is developed that will allow us to explore different VM scheduling strategies in distributed cloud federations. This model can be used as a template to investigate complex cloud federation scenarios using the multi-level scheduler presented here.

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In recent years, cloud federations have gained popularity. Small as well as big cloud service providers (CSPs) join federations to reduce their costs, and also cloud management software like OpenStack offers support for federations. In a federation, individual CSPs cooperate such that they can move load to partner clouds at high peaks and possibly offer a wider range of services to their customers. Research in this area addresses the organization of such federations and strategies that CSPs can apply to increase their profit. In this paper we present the latest extensions to the FederatedCloudSim framework that considerably improve the simulation and evaluation of cloud federations. These simulations include service-level agreements (SLAs), scheduling and brokering strategies on various levels, the use of real-world cloud workload traces and a fine-grained financial evaluation using the new CloudAccount module. We use FederatedCloudSim to compare scheduling and brokering strategies on the federation level. Among them are new strategies that conduct auctions or consult a reliance factor to select an appropriate federated partner for running outsourced virtual machines. Our results show that choosing the right strategy has a significant impact on SLA compliance and revenue.

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