Ordering Upgrade Changes for Highly Available Component Based Systems

Highly available systems undergo upgrades like any other systems but with a more stringent requirement of no or very limited service outage. Unforeseen violations of software dependencies are the main causes of service outage during upgrade. We investigate the problem in the case of component based systems, more specifically systems managed by an SAForum compliant middleware. We discuss dependencies identified so far and propose a method to order the upgrade changes into stages to respect the constraints imposed by these dependencies and therefore limit service outage.