Hybrid cloud, by definition, means that the design spans more than one cloud. An example of this kind of architecture may include a situation in which the design involves more than one OpenStack cloud (for example, an OpenStack-based private cloud and an OpenStack-based public cloud), or it may be a situation incorporating an OpenStack cloud and a non-OpenStack cloud (for example, an OpenStack-based private cloud that interacts with Amazon Web Services). Bursting into an external cloud is the practice of creating new instances to alleviate extra load where there is no available capacity in the private cloud. Some situations that could involve hybrid cloud architecture include: Bursting from a private cloud to a public cloud Disaster recovery Development and testing Federated cloud, enabling users to choose resources from multiple providers Hybrid clouds built to support legacy systems as they transition to cloud As a hybrid cloud design deals with systems that are outside of the control of the cloud architect or organization, a hybrid cloud architecture requires considering aspects of the architecture that might not have otherwise been necessary. For example, the design may need to deal with hardware, software, and APIs under the control of a separate organization. Similarly, the degree to which the architecture is OpenStack-based will have an effect on the cloud operator or cloud consumer's ability to accomplish tasks with native OpenStack tools. By definition, this is a situation in which no single cloud can provide all of the necessary functionality. In order to manage the entire system, users, operators and consumers will need an overarching tool known as a cloud management platform (CMP). Any organization that is working with multiple clouds already has a CMP, even if that CMP is the operator who logs into an external web portal and launches a public cloud instance. There are commercially available options, such as Rightscale, and open source options, such as ManageIQ (http://manageiq.org), but there is no single CMP that can address all needs in all scenarios. Whereas most of the sections of this book talk about the aspects of OpenStack, an architect needs to consider when designing an OpenStack architecture. This section will also discuss the things the architect must address when choosing or building a CMP to run a hybrid cloud design, even if the CMP will be a manually built solution.