Socket-level redirection mechanism for scalable internet server system

Abstract

With the explosive growth of the Internet, a single server is no longer sufficient to handle the requested load for a site. Server replication is an approach often used to improve the ability of a site to deal with a large number of clients. A lot of schemes have been developed to provide transparent access to the replicated servers. Existing schemes mostly need specialized hardware devices or the modification of the operating system of the client or the server with high cost. In these methods, to provide user-transparency, all redirected packets must be rewritten by mapping original server address into selected server address with additional overhead. And in other methods such as HTTP redirection, even though packet rewriting is not needed, the latency of redirection to selected server makes users experience slower response time. In this paper, we propose a new scheme, socket-level redirection (SLR) mechanism. Its main idea is to redirect a client request to a replicated server in the socket function of the client. This mechanism only requires the modification of the socket library of the client and does not include the overhead of packet rewriting at all because redirection is achieved in socket-level. Furthermore, since redirection protocol is based on UDP, the latency overhead of redirection can be minimized to one round trip time. We describe the redirection mechanism in detail and the performance of the mechanism is evaluated by experiments over the Internet. These experiments showed that by our redirection mechanism, pages from web sites could be transferred 2-5 times faster than round-robin DNS(RR-DNS), while the increased latency by redirection was negligible.