Globally Consistent Dynamic Reconfiguration

The evolution of distributed applications to reflect structural changes or to adapt to specific conditions of the run-time environment is a difficult issue especially if continuous service is required from end-users. This latter constraint implies to perform changes with minimal penalty on the service provisioning. The set of tools and services that allow such a goal to be achieved is usually designated as dynamic reconfiguration capabilities. A major issue related to dynamic reconfiguration is to ensure applications consistency after a reconfiguration. In most of the previous works, only local consistency has been addressed, i.e. reconfiguration only ensures consistency of the components state and of the communication channels. In this paper, we argue that local consistency is not sufficient and that consistency of global computations must be ensured. The global computation is generally composed of sessions which should be isolated with respect to reconfiguration. We observed that sessions isolation is similar to transactions isolation, and we therefore propose to use an extended transaction model in order to ensure global consistency when a reconfiguration occurs. We then discuss possible solutions for non transactional applications.