  Cloud computing promises a radical shift in the provisioning of computing
resource within the enterprise. This paper describes the challenges that
decision makers face when assessing the feasibility of the adoption of cloud
computing in their organisations, and describes our Cloud Adoption Toolkit,
which has been developed to support this process. The toolkit provides a
framework to support decision makers in identifying their concerns, and
matching these concerns to appropriate tools/techniques that can be used to
address them. Cost Modeling is the most mature tool in the toolkit, and this
paper shows its effectiveness by demonstrating how practitioners can use it to
examine the costs of deploying their IT systems on the cloud. The Cost Modeling
tool is evaluated using a case study of an organization that is considering the
migration of some of its IT systems to the cloud. The case study shows that
running systems on the cloud using a traditional "always on" approach can be
less cost effective, and the elastic nature of the cloud has to be used to
reduce costs. Therefore, decision makers have to be able to model the
variations in resource usage and their systems deployment options to obtain
accurate cost estimates.
