Towards an Elasticity Framework for Legacy Highly Available Applications in the Cloud

Elasticity is a key characteristic of cloud computing where the provisioning of resources can be directly proportional to the runtime demand. Legacy highly available applications typically rely on the underlying platform to manage their availability by monitoring heartbeats, executing recoveries, and attempting repairs to bring the system back to normal. Migrating such applications to the cloud can be particularly challenging, especially if the elasticity policies target the application only, without considering the underlying platform contributing to its high availability (HA). In this paper, we present a comprehensive framework for the elasticity of highly available applications that considers the elastic deployment of the platform and the HA placement of the application's components. We apply our approach to an IP multimedia subsystem (IMS) application and demonstrate how, within a matter of seconds, the IMS application can be scaled up while maintaining its HA status.