As much as OpenStack promised a utopian future where an application could be written once and target multiple clouds that run OpenStack, the reality was that vendor choice leaked through the abstractions to the point where the end user must know about deployment and configuration details, compromising interoperability and favoring vendor lock-in. Shade is a middleware written in Python by the OpenStack community which stands between users and clouds, abstracting vendor differences in order to

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... low a seamless experience in multi-cloud environments. It is widely used by OpenStack Continuous Integration systems nowadays, booting thousands of servers every day in numerous deployments distributed around the globe. This paper enumerates, categorizes and exemplifies the interoperability issues found in OpenStack deployments and then describes how Shade addresses most of them.