Model-based techniques for QoS assessment of cloud-hosted CDN services

Given cloud-based realization of a CDN service S (i.e., Content Distribution Network), QoS auditing captures the QoS violations that arise under various resource depletion and outage scenarios faced by S. Third-party control of the underlying cloud VM and storage nodes hosting the content (i.e., proxies of content server) raises the issue of reasoning about how well the CDN internal mechanisms are engineered to offer a required level of service to the application (i.e., low latency and overhead). We employ computational models of S to determine the optimal feasible proxy placements in the CDN topology and verify how close is the actual behavior of S to this 'gold standard'. Using declarative specifications, the QoS meta-data and CDN adaptation processes of S are externalized to enable a management module H reason about QoS violations. The paper elucidates the software and system engineering issues that arise in an external evaluation of the QoS provisioning of S by H.