Traps on the Way from OSGi to Distributed OSGi

OSGi is a powerful technology for an application life cycle management. It deals with configuration and change management and helps to build quality service oriented systems. OSGi is pretty popular framework with broad applicability and many mature implementations. Eclipse IDE is maybe the most commonly used example of application build with OSGi.

This sounds very good, but current OSGi standard deals only applications running in the single JVM. It is obvious that the latest trends with scaling everything out diminish the value of this great technology to a large degree. So, there is no surprise that third party frameworks, built on top of OSGi, appeared on the horizon. Newton and R-OSGi are maybe the most well-known ones. From the OSGi side, latest drafts of the standard include specification of Distributed OSGi also known as RFC 119. As far as I know, there is no production-ready implementation of this RFC, but there were successful demos, and the RFC itself is very mature at the moment. All of these approaches to distribute OSGi are really interesting and worth discussing, but for now I am not going to dive deep into them.

The thing I am aware of at the moment is that OSGi is essentially just a framework for module (or component) management. When it deals with components in one JVM, everything is good. But moving to distribute environment will bring many new problems, like the need of communication medium between components. The desire (or need) to implement yet another RMI as a part of OSGi can be very strong. However, in my opinion, this should be avoided soever. OSGi is not a communication technology - there are lot of them on the market, covering different areas and created for different purposes. Implementing a new one, which will cover all required ways of communication, is hard. Distributed OSGi, on the opposite, should not cover this topic at all, dealing only with what OSGi deals the best - managing modules lifecycle, but in a distribute fashion. In the ideal situation , developers should have free choice of communication medium between modules, according to the requirements of the project.

This problem touches not only me, but the good news are that it seems creators of RFC 119 are on the right way. Other technologies for distributing OSGi are not so good from this point of view: R-OSGi introduces custom communication medium, and Newton makes use of Jini and RMI. It is not exactly bad for them, because they maybe can solve other problems better and they are ready to use right now, unlike RFC 119.

Actually, to correctly and objectively compare these technologies, additional research is required and it is not the goal of this post. If somebody is interested in the topic, Hal Hildebrand's blog can be used as a great source of an interesting information about RFC 119, OSGi in general, and in particularly, comparison of R-OSGi and Distributed OSGi.