There is an increasing number of cloud platforms emerging in both academia and industry. They often federate resources from multiple infrastructures in order to benefit from the unique features that each presents. After introducing the main capabilities and features of OpenStack, this article addresses the integration of OpenStack-based platforms into larger, heterogeneous multi-cloud infrastructures, taking the EU FP7 BonFIRE project as an integration use case. Ultimately, we aim to contribute to the state of the art and provide guidelines to integrators looking to federate Open Stack testbeds into more complex architectures.