Is there an elegant way to use Services across or between OSGi containers?
Is it even possible?
For instance, lets say I have a service interface on my local machine. What methodologies/technologies can I use to get that service interface accessible through a remote OSGi container's BundleContext?
It is possible, but there are no libraries (afaik) that will do this for you. I've rolled my own for my current job. OSGi runtime on client and server, RMI is the transport. I've had to make HEAVY use of Proxy objects.
Register a service in the server's OSGi runtime (Equinox). I have a listener that watches all services looking for a property/attribute indicating this service should be exported (made remote), something like "remotable=true". It's easy to filter using the ServiceTracker. Over RMI I instruct the client to create a Proxy object with the service interface. All calls to this proxy object are generically send back over RMI (a call like execService serviceid, method name, var args params) and then invoked on the REAL service.
I've left out some of the low level details, but you can probably sort it out. If you can stray away from RMI, you may want to look into Riena (there may even be a way to write an RMI transport for Riena, I just haven't bothered to try)
It's not very clear what you are trying to achieve. You have got a service, you can access it using RMI, and you need to available as an OSGi service?
I guess you could write an interface to you local machine service. You could then write a bundle that connectes to that service and exposes that interface in the OSGi service registry. Then, your main bundle could locate that service using the interface name or service name.
It shouldn't be too much work to get an RMI connection to your local service. Maybe some config options to establish the initial connection. It might be important to write a facade for your service before you publish it in OSGi, in order to achieve some form of decoupling, and perhaps to hide the fact that it is an RMI service.
But then maybe I completely misunderstood you and all this is useless.
There is a RFC called Remote Services (formerly Distributed OSGi) that does exactly what you are trying to achieve. The RFC is almost completed, and there are already 2 implementations provided respectively by Apache CXF and Eclipse ECF.
Both the implementations allows to do transparent remoting of an OSGi service. You just have to define the OSGi service as usual, and add some configuration parameters to make it a remote service.
As well as CXF above, there's also Eclipse ECF, which is a collection of communication frameworks and provies an early implementation of the OSGi 4.2 remote services (aka distributed OSGi). It works by registering a local service to which your client binds in the VM, then creates a proxy on the remote machine, and using a technology of your choice (RMI, WebServices etc.) can remote the calls.
Obviously this uses by-value method invocation syntax (which your service needs to know about) but other than that, any comms errors are RuntimeException.