Engineering fault-tolerant TCP/IP servers using FT-TCP

In a recent paper [2] we have proposed FT-TCP: an architecture that allows a replicated service to survive crashes without breaking its TCP connections. FT-TCP is attractive in principle because it does not require modifications to the TCP protocol and does not affect any of the software running on the clients; however, its practicality for realworld applications remains to be proven. In this paper, we report on our experience in engineering FT-TCP for two such applications—the Samba file server and a multimedia streaming server from Apple. We compare two implementations of FT-TCP, one based on primary-backup and another based on message logging, focusing on scalability, failover time, and application transparency. Our experiments suggest that FT-TCP is a practicable approach for replicating TCP/IP-based services that incurs low overhead on throughput, scales well as the number of clients increases, and allows recovery of the service in near-optimal time.