Cloud infrastructures are now widely adopted across technology industries and research institutions. However, single cloud providers may not fully satisfy more complex user requirements, and to cope with them, a solution that do not rely on a single cloud environment but instead allow resource provisioning from external providers is required. As a result, in the recent years there has been a growing interest in developing hybrid cloud solutions that bind together distinct and heterogeneous cloud infrastructures. In this paper we will describe the orchestration approach for heterogeneous clouds being implemented within the INDIGO-DataCloud project, based on the OASIS Topology and Specification for Cloud Applications (TOSCA) standard
