The National Institute of Standards and Technology defines hybrid cloud as “a composition of two or more clouds (private, community or public) that remain unique entities but are bound together, offering the benefits of multiple deployment models.” Although this definition sounds very reasonable, it does not cover all aspects of hybrid clouds.
Let’s discuss possible deployment models first. There are five defined cloud deployment models, from a private cloud on-premises to a public cloud service with a cloud service provider.
Often, hybrid cloud refers to a combination of a public cloud service and a private cloud on-premises; however, hybrid clouds could also consist of two public clouds provided by different providers or even a combination of a cloud and traditional IT. Actually, a setup where existing systems on a traditional IT infrastructure are combined with a public cloud service is currently the most frequent use case of a hybrid cloud.
Any hybrid cloud setup has some challenges that need to be considered during the planning and design phase:
- The most obvious challenge is network connectivity, especially if remote cloud services like a public cloud or a hosted private cloud are involved. Not only must bandwidth, latency, reliability and associated cost considerations be taken into account, but also the logical network topology must be carefully designed (networks, routing, firewalls).
- Another huge challenge is the manageability of different cloud services. When different cloud services are used, every service provider will have its own management and provisioning environment. Those environments can be considered completely independent from each other. By having instances in different cloud services, there is no complete picture available showing the number of totally deployed instances and their statuses. An orchestration layer can be a possible solution for this problem. This layer provides a single interface for all cloud-related tasks. The orchestration layer itself communicates with the different cloud services through application programming interfaces (APIs). The big advantage of an orchestration layer is the ability to track and control activities on a central point to maintain the big picture.
- Today, plenty of cloud service providers maintain their own proprietary set of APIs. This makes the use of orchestration very complex as the orchestrator requires some kind of a driver component for each proprietary API set. However, the trend of standardized APIs is clearly seen in the industry. OpenStack seems to be the future cloud industry standard.
Hybrid clouds mainly work on an infrastructure and application level. On the infrastructure layer, a hybrid cloud means the combination of virtual machines from different cloud services. On the application or software as a service (SaaS) layer, a hybrid cloud describes an application setup with components in different SaaS offerings or existing applications within the data center of an enterprise. The challenge on an SaaS-based hybrid cloud is mainly the exchange of data between the different services and applications. Like orchestration works on the infrastructure level, data integrators work on the application layer.
A hybrid cloud is a combination of different clouds, be it private, public or a mix. The biggest challenge is the integration of the different cloud services and technologies. Standardized APIs such as OpenStack seem to solve most of those issues.