What is necessary to achieve interoperability in the Cloud?
As described in the previous sections, 3 major interoperability approaches arise. First, there is the standardisation approach, next there is the middleware approach and last but not least there is the API approach. This is also supported by [Hof09] and [Gov10]. In addition to that, [Gov10] suggests building abstraction layers in order to achieve interoperability and transportability.
There are two main aspects where interoperability is necessary. One level is the management level. This deals with handling the virtual machine(s), applying load balancing, setting DNS settings, auto scaling features and other tasks that come with IaaS solutions. However, this level is mainly necessary in IaaS solutions as PaaS solutions already take care of most of it. The other level is the services level. The services level is basically everything that comes with application services such as messaging, data storage and databases.
Figure: Cloud interoperability approaches
These requirements are described in several relevant papers such as [End10], [Mel09], [Jha09].
Parameswaran et al. describes similar challenges for Cloud interoperability. The authors see two different approaches, the first via a unified cloud interface (UCI) and the second via Enterprise Cloud Orchestration [Par09].
A unified cloud interface is basically an API that is written “around” other cloud APIs that is vendor specific. It requires some re-writing of and integration. This is similar to the approach selected by Apache jClouds and Apache libcloud.
The Enterprise Cloud Orchestration is a layer where different cloud providers register their services. The platform then provides these services for users like in a discovery. This is very similar to UDDI. The downside of this is that the orchestration layer still needs to integrate all different services (and built wrappers around them). However, it is transparent to the end-user.
Figure: Enterprise Orchestration Layer [Par09]