We present the design and implementation of Hydra, a peer-to-peer architecture for massively-multiplayer online games. By supporting a novel augmented server-client programming model with a protocol that guarantees consistency in the messages committed when nodes fail, existing game developers can realize the benefits of a peer-to-peer architecture without the burden of handling the complexities associated with network churn. Our key contribution is the development of a programming interface that is intuitive and easy to use, and that can be supported transparently at the network layer. We have implemented a prototype of Hydra and we demonstrate that our proposed architecture is practical by developing two games under the Hydra framework: a simple "capture the flag" tank game and a squad-based real-time strategy (RTS) game. Our experience in developing these games suggests that our proposed programming model is suitable for game development. Our preliminary experiments also show that Hydra imposes only a small message overhead and is thus scalable.