Dynamic replica placement in content delivery networks

The content delivery networks (CDN) paradigm is based on the idea to transparently move third-party content closer to the users. More specifically, content is replicated on CDN servers which are located close to the final users, and user requests are redirected to the "best" replica (e.g. the closest) in a transparent way, so that users perceive a better content access service. In this paper we address the problem of dynamic replica placement. Being dynamic, our solutions adoptively select the number of replicas for each content and the replicas positions to account for traffic requests dynamics. The schemes we propose are designed to minimize the overall cost paid by the CDN provider (for replicas placement, removal, and maintenance) without degrading the quality of the users perceived access service. The contributions of the paper are twofold. First we introduce a centralized and distributed scheme for replica placement in a dynamic traffic scenario. Then, by means of a simulation based performance evaluation, we assess the effectiveness of the proposed schemes, and compare their performance with static solutions which have been proven to perform well in the literature. Simulation results show that both the two proposed algorithms achieve very good performance, resulting in a significant improvement over the static solutions. Despite relying on local information only, the distributed scheme has comparable performance to the centralized one. Both the two schemes result in low average distance between the users and their serving replicas, in low average number of replicas, in infrequent replicas add and tear down, and in high probability of being able to serve a request.