This study describes a new approach to cloud federation architecture for academic community cloud. Two basic approaches have been proposed to deal with cloud burst, disaster recovery, business continuity, etc., in community clouds: standardization of cloud services and multi-cloud federation. The standardization approach would take time; i.e., it would not be effective until there are enough implementations and deployments following the standard specifications. The federation approach places limitations on the functionalities provided to users; they have to be the greatest common divisor of the clouds' functions. Our approach is "cloud on demand", which means on-demand cloud extension deployments at remote sites for inter-cloud collaborations. Because we can separate the governance of physical resources for cloud deployment and the governance of each cloud by this approach, each organization can have full control on its cloud. We describe how the problems of the previous approaches are solved by the new approach and evaluate a prototype implementation of our approach.