Consistently applying updates to compositions of distributed OSGi modules

Updating software at runtime is a challenge that covers various aspects of software design and runtime systems. The OSGi Alliance has proposed and standardized a runtime system for composing Java applications out of modules, the OSGi Framework. The possibility to update modules at runtime and thereby dynamically change the application has been an intrinsic design decision of the framework architecture. With recent approaches to extend the OSGi model from single Java virtual machines to distributed systems, however, updates no longer only affect a single machine in the system. The specifications of OSGi and the upcoming proposals for distributed OSGi services do not answer the question how to consistently apply updates in such environments. In this paper, we explore a solution based on our R-OSGi system. We show how to extend the existing (local) OSGi update mechanism to consistently apply updates to multiple nodes of a distributed OSGi application.