Harvesting dispersed computational resources is nowadays an important and strategic topic especially in an environment, like the computational science one, where computing needs constantly increase. On the other hand managing dispersed resources might not be neither an easy task not costly effective. We successfully explored the use of OpenStack middleware to achieve this objective, our man goal is not only the resource harvesting but also to provide a modern paradigm of computing and data usage access. In the present work we will illustrate a real example on how to build a geographically distributed cloud to share and manage computing and storage resources, owned by heterogeneous cooperating entities