How CLEVER-based clouds conceive horizontal and vertical federations

Nowadays, the cloud computing ecosystem includes hundreds of independent and heterogeneous clouds. Most of such cloud platforms can be considered as "islands in the ocean of the cloud computing" and do not present any form of federation. At the same time several clouds are beginning to use the cloud-based services of other clouds, but there is still a long way to go toward the establishment of a worldwide ecosystem including thousands of cooperation federated clouds. This paper aims to investigate the existing cloud middleware solutions able to address all the potential issues involved in these new cloud scenarios. In particular, the CLEVER cloud middleware will be analyzed, highlighting its design and features, and explaining the motivations that allow us to consider it suitable to the different phases of the evolution of federated cloud computing.