The popular Squid proxy daemon comes with a facility that allows a single server to act as a front end to web servers [OP97]. This works by having clients connect to the Squid server as if it were an HTTP server and then farming requests off to the real web server or servers. This can be used to share load around multiple servers on high volume sites, as illustrated in Figure 3 or to protect HTTP servers that contain sensitive data by placing them behind a firewall such that the Squid server can access the HTTP server but other hosts on the Internet can not.
Though primarily intended to allow load sharing on high volume sites this can also be used to provide some form of redundancy. The HTTP accelerator server can be a front end for multiple back end http servers hence the loss of a HTTP server should not result in a site being down. And of course as the http accelerator itself has no content is can be backed up using the ARP base method of creating redundant servers. On small sites this extra layer between users and the web server may just be another potential point of failure however the switching idea presented is an interesting one.