Cloud computing provides new facilities for building elaborated services hosted through various infrastructures over the Internet. In the meantime, these ones pose new important challenges in terms of security due to their intrinsic nature. We propose in this paper to detail a software-defined security framework supporting the protection of these services, in the context of distributed cloud. These ones require security mechanisms able to cope with their multi-tenancy and multi-cloud properties. The foundations of this framework rely on the software-defined logic to express and propagate security policies to the considered cloud resources, and on the autonomic paradigm to dynamically configure and adjust these mechanisms to distributed cloud constraints. In particular, we describe the main components and protocols of this software-defined security framework, evaluate this one and discuss implementation considerations, through the analysis of different realistic scenarios.