OSGi goes beyond service invocations in a single JVM with the introduction of RFC 119 - Distributed OSGi. It will enable an OSGi bundle deployed in a JVM to invoke a service (either OSGi or non-OSGi) in another JVM or process, potentially on a remote computer accessed via a network protocol. Meanwhile, an OSGi service deployed in another JVM or a non-OSGi program such as Web Service client, potentially on a remote computer, to find and access a service running in the "local" OSGi JVM (i.e. an OSGi deployment can accept service invocations from remote OSGi bundle or external environments). The distributed computing functionality is added to the OSGi programming model without additional APIs or concepts as the distribution layer will be mostly transparent to OSGi developers by configuration.
SCA (Service Component Architecture) provides a technology-neutral approach to abstract business logic into components and assemble them into composite applications. It greatly simplifies the component communications using declarative bindings. QoS requirements can be uniformly declared as SCA intents which can be mapped and realized using different stacks. SCA is a great fit to be a distribution provider for distributed OSGi.
Apache Tuscany is an open source project that implements the SCA specifications. It provides integrations of implementation types (such as Java, Scripting, BPEL, Spring, OSGi and JEE) and binding types (such as Web Service, JMS, EJB, CORBA, RMI, JSONRPC, and ATOM) as the infrastructure for SCA programming. The latest version of Tuscany runtime is fully built on top of OSGi as the foundation. We recently added the OSGi RFC 119 support.
In this session, we will teach you how to develop a distributed OSGi application to leverage the SCA capabilities using Apache Tuscany. A calculator scenario will be used to demonstrate the distributed OSGi service invocations using RMI and Web Service protocols. We will also explain how to model an OSGi bundle as an SCA component and configure the SCA composite to provide communications between services. The readers will understand the basic ideas behind distributed OSGi in the concrete example and the power of Tuscany SCA for service composition.