As discussed in the previous sections, there are several standards and interoperability frameworks available. Most of them are infrastructure related. The standards and frameworks can generally be clustered into 3 groups.
The first group is the “Standards” group, which consists of OCCI an the DMTF standards. The second group is the “Middleware” group. This group contains mOSAIC, the PaaS Semantic Interoperability Framework and Frascati. The third group is the “Library” group. This group is a concrete implementation that provides a common API for several cloud platforms. The two projects in here are Apache jClouds and Apache libcloud.
Figure: Interoperability in the Cloud
OCCI provides great capabilities for infrastructure solutions, but there is nothing done for individual services. The same applies to the standards proposed by the distributed management task force.
As with the libraries and frameworks, a similar picture is drawn. Apache jClouds and Apache libcloud provide some interoperability features for infrastructure services. As for platform services, only the blob storage is available. When developers build their applications, they still run into interoperability challenges.
mOSAIC offers a large number of languages and services, however, it is necessary to build a layer on top of an existing platform. This is not a lightweight solution, as a developer has to maintain both – the developed application and the middleware solution installed on top of the provider. The developer eliminates the vendor lock-in, but runs into operational management of the mOSAIC platform. This eliminates a problem on the one side but might create a new one on the other side.
The same problem exists with the PaaS Semantic Interoperability Framework. A user has to install a software on top of the cloud platforms, which then has to be maintained by the user. The goal of platform as a service is to relieve the user from any operational management like in IaaS platforms. Frascati is also a middleware that needs to be maintained.
All of the libraries or frameworks described work for IaaS services. None of them support the PaaS paradigm and services related to it. Apache libcloud and Apache jClouds offer some very fundamental support for the storage service. However, other services such as messaging and key/value storage are not supported.