Web++: An Architecture for Replication of Web Resources

We describe the design of a system for a fast and reliable HTTP service termed Web++. Web++ achieves high reliability by dynamically replicating Web data among multiple Web servers. Web++ selects a server which is available and that is expected to provide the fastest response time. Furthermore, Web++ guarantees data delivery, provided that at least one server containing the requested data is available. After detecting a server failure, Web++ client requests are satisfied transparently to the client by another server. Furthermore, the Web++ architecture is flexible enough for implementing additional performance optimizations. We describe implementation of one such optimization, batch resource transmission, whereby all resources embedded in an HTML page that are not cached by the client are sent to the client in a single response. Web++ is built on top of the standard HTTP protocol and does not require any changes either in existing Web browsers, or the installation of any software on the client side. In particular, Web++ clients are dynamically downloaded to Web browsers as signed Java applets. We implemented a Web++ prototype; performance experiments indicate that Web++ system with 3 servers improves the response time perceived by clients on average by 36.6%, and in many cases by as much as 59%, when compared with the current Web performance. In addition, we show that batch resource transmission can improve the response time on average by 37% for clients with fast network connections and 29% for the clients with 56 Kb modem connections.