Java Open Source Framework for Service Management

Question

Working on a Java-based large distributed system, so there will be multiple services running across multiple machines .....

Looking for an open source framework to be able to manage these services(e.g. start/stop a service, install a new a service remotely etc.)

Apache Karaf seems to be a good choice, but underneath it uses apache felix (an OSGi reference implementation) bundle which I have a hard time to really understand. In particular, it seems to be easy to define and register a service in felix, but how do you invoke such a service remotely? Do you need to have a separate RPC mechanism to achieve that? There seems to be very few links describe it. In general how do people use OSGi? Is Apache felix out of date?

Any other framework that can be used to manage services assuming I will have my own RPC layer (say RMI based or Netty based)?

Answer 1

I guess you have to specify the way you define a service. There are services, like remote services that use RPC mechanism, for example EJB remote calls. Another way to define services is to talk of Web-Services, either using SOAP(XML) or JAXRS(JSON) as transport protocol. And there is the definition of services in OSGi which just means a separation of API (service definition) and implementation. As sum-up you could define OSGi as a SOA for Applications within the same VirtualMachine. (it gives much more, but this is one way to look at it from a service perspective)

Apache Karaf is a OSGi server that is comparable to a Application Server, only it works for OSGi applications. It brings a lot of convenience technologies on top of a choosable OSGi framework. That would be either Apache Felix or Eclipse Equinox. Both are OSGi frameworks that provide the basic OSGi infrastructure - SOA in the same JVM.
Now there are a lot of other benefits of it, like starting and stoping services, updating services.

Taking the RPC into account this can easily be achieved, by combining OSGi-Services with CXF for example. It can easily be configured to export an OSGi service as CXF service. (this is very Karaf/CXF specific)

Apache Karaf itself also supports clustering with Apache Karaf Cellar, which also provides a DOSGi service for easier communication of services across cluster groups. DOSGi stands for Distributed OSGi, which can also be achieved by using CXF and much other implementations.

Apache Felix and OSGi in general are far away of being out-of-date. A lot of Java EE Application servers use OSGi as their underlying technology to be modular and have a smaller footprint.
That would be GlassFish, Websphere, Geronimo etc...