This paper deals with Cloud federation issues, where Clouds are both providers and clients of virtual resource at the same time. Specifically, we have designed a solution based on a XMPP communication platform, which allows to set up federated environments and to easily manage virtual shared resources. Heterogeneous and dynamic Clouds can interact in near-real time, making available their own resources according to specific agreement policies. We are thinking to implement the proposed solution using the Hadoop framework, a well-known Cloud Map-Reduce middleware designed to offer different types of services. Here, we analyze the basic and useful elements necessary to making up federated clouds. By mean of Cloud federation, two or more Hadoop clusters can be connected in order to increase service scalability, overcoming some technical limitations of the Hadoop framework itself.