Dynamic Replica Placement in Content Delivery Network

The Content Delivery Networks (CDN) paradigm is based on the idea to move third-party content closer to the users transparently. More specifically, content is replicated on servers closer to the users, and users requests are redirected to the best replica in a transparent way, so that the user perceives better content access service. In this paper we address the problem of dynamic replica placement and user requests redirection jointly. Our approach accounts for users demand variability and server constraints, and minimizes the costs paid by a CDN provider without degrading the quality of the user perceived access service. A non-linear integer programming formulation is given for the replica placement and user request redirection problems. The output of the model is the periodic determination of the new location of replicas based on traffic estimates and the current replica locations. The actual solution is obtained by mapping the non-linear integer problem into a series of mixed integer linear problems obtained by linearizing the non-linear constraints of the original problem. Preliminary numerical results show that the proposed solution is capable of effectively limiting the percentage of unsatisfied requests without over-replicating the contents over the CDN servers.