Enhanced server fault-tolerance for improved user experience

Interactive applications such as email, calendar, and maps are migrating from local desktop machines to data centers due to the many advantages offered by such a computing environment. Furthermore, this trend is creating a marked increase in the deployment of servers at data centers. To ride the price/performance curves for CPU, memory and other hardware, inexpensive commodity machines are the most cost effective choices for a data center. However, due to low availability numbers of these machines, the probability of server failures is relatively high. Server failures can in turn cause service outages, degrade user experience and eventually result in lost revenue for businesses. We propose a TCP splice-based Web server architecture that seamlessly tolerates both Web proxy and backend server failures. The client TCP connection and sessions are preserved, and failover to alternate servers in case of server failures is fast and client transparent. The architecture provides support for both deterministic and non-deterministic server applications. A prototype of this architecture has been implemented in Linux, and the paper presents detailed performance results for a PHP-based Webmail application deployed over this architecture.