Content distribution networks (CDNs) improve the performance of content delivery by replicating the popular content on surrogate servers deployed at the edge of the Internet. The CDN-P2P architecture, which combines the complementary advantages of both CDN and P2P networks, can improve the quality of service (QoS). In this paper, we propose a k-coordinated decentralized replica placement algorithm (DRPA) based on a gain formulation of the replica placement problem. Although the gain formulation is designed for different types of the CDN-P2P architecture, we focus on the robust ring-based architecture in this study. In our approach, each surrogate server makes the replica placement in terms of the content replicas on k closer surrogate servers, which enhances the system scalability compared to the centralized replica placement heuristics. In addition, according to the simulation results, the proposed algorithm is able to reduce the backbone traffic between the servers and the requesting peers compared to the traditional replica placement algorithms for the pure CDN.