Discovery-based SCA Domain for OSGi RFC 119

[Raymond Feng]

Hi,

We have been discussing the idea to use p2p protocols to manage an SCA 
domain. There are some interesting use cases coming up as I look into the 
dynamicity perspective for the OSGi RFC 119 implementation using 
Tuscany/SCA.

To use SCA domain to manage a collection of OSGi frameworks so that the OSGi 
services can see each other as follows:

1) Discover remote OSGi services provided by other OSGi frameworks. In SCA 
term, the information about the published services (domain-level component 
services) is managed by the SCA domain. The service metadata of interest is 
the service endpoints, associated properties and policies. Such data can be 
exchanged across the nodes using a p2p or centralized coordinator.

2) Synchronize between the OSGi frameworks for the states of the services 
via the SCA domain. For example, if a property for a remote OSGi service 
exposed to SCA domain is updated, the change will be reflected to the OSGi 
service which is an SCA proxy in the client-side OSGi service registry.

In OSGi, we look up the service references from the service registry with 
the name of the service interface together with a LDAP-style filter which 
matches against the service properties. Mapping to SCA, it's like the 
domain-level autowiring or wiredByImpl which allows the references to be 
resolved within the SCA domain with some matching criteria.

As the starting point, I'm thinking of making the SCA service registry 
remotely accessible. It can serve the service descriptions to SCA nodes or 
clients. The service registry can be managed by an SCA domain manager which 
receives publication of services from the nodes. The other option is to use 
p2p protocol to build a distributed group of the nodes and exchange the 
service metadata within the group. With a distributed service registry, we 
can resolve the SCA references which uses the SCA wiring 
(componentName/serviceName/bindingName) within the SCA domain. It also 
allows us to deal with domain-level autowiring.

I start to play Tomcat Tribes which provides a set of simple APIs to use IP 
Multicast to build a group of members. I got a Tribe sample working in my 
environment. The other interesting project is ZooKeeper from Apache Hadoop 
(http://hadoop.apache.org/zookeeper/). We will use the Extension 
Point/Extension pattern to make the p2p layer pluggable.

Thoughts?

Thanks,
Raymond