OSGi in Distributed Infrastructures

Question

We're working on an OSGi-based infrastructure for processing stream-based data flows. Specific processing tasks are executed by individual OSGi components. We now need the possibility to distribute those components over different machines, which means, we need some kind of communication mechanism between OSGi components/containers.

During my research I came across different potential solutions: R-OSGi, Apache CXF for Distributed OSGi, Eclipse Communication Framework.

ECF seems particularly interesting as it supports different transports formats and provides support for stuff like service discovery.

My central questions:

• Are there any detailed tutorials/walk-throughs for setting up an ECF infrastructure within Felix? (from my research, I found, that Felix support has been added recently)
• Are there any solutions besides the three listed above which I might have missed?
• Is there a reason for taking Apache CXF instead of ECF?

Answer 1

The first question -- whether there is a detailed walk-through for setting up ECF with Felix -- I don't know the answer to, though one might use a search engine to find out combinations of those terms.

The problem is ECF uses the Equinox infrastructure, and has at times inadvertently relied on packages that are non-public through transitive dependencies (particularly the Runtime API which uses Equinox for non-public debugging). This, in turn, means that ECF relies on a whole host of other components to be available and it's this set which typically isn't well defined on a Felix runtime.

You have missed out Paremus' Service Fabric, which is a commercial OSGi cloud solution. I'm not sure if you were specifically focussing on open-source or not; but if you are including commercial licenses then they have a very robust architecture for remote services.

Finally, the Apache CXF over ECF question -- if you're using Felix, I'd argue that going with Apache CXF is probably easier than going with ECF. This is mainly due to the dependency set and getting it working, combined with the fact that ECF may not be tested on Felix and so may assume particular aspects of the Equinox runtime (which includes, for example, the runtime's parent classloader delegation to pick up things on the boot classpath). This isn't really the fault of ECF per se, but rather an artefact of how the Eclipse ecosystem works.

If you want to communicate with non-OSGi runtimes, there's an advantage in the Apache CXF in that they can generate WDSL for interaction with other languages. I believe that you can do the same thing in ECF with a bit more work. The CXF solution is likely to be more verbose than a corresponding ECF one (WSDL always is) but if you're not using high volumes of requests this isn't likely to make a significant difference.