Once Is Not Enough
As to communications lines, the best thing a site can do is to have big enough pipes. That translates into having enough bandwidth available and, in the case of the larger sites, redundant communications lines.
Unfortunately, redundant lines won't always protect a site when a backhoe takes out the data lines or an upstream router flakes out.
That's why companies like AT&T and Exodus Communications have multiple hosting centres located throughout the world. If one site goes down, other sites pick up the load.
Another "push-to-the-edge" strategy involves installing caching servers on various ISP or backbone networks in different geographic locations. As a chunk of hardware, caching servers run about US$10,000 each and can be clustered.
Having more than one Web site means you must direct incoming traffic to the best site. The intelligence must factor in not just the requester's or site/cache's locations, but also network congestion and traffic conditions at each site. In other words, the closest Web site is not always the best choice. F5 provides such front-end intelligence in its 3DNS box for about US$35,000.
Keeping content up-to-date on all sites also requires a publishing system that tracks and replicates the changed pages from the originating Web site to the secondary Web sites. Figure about another US$30,000 for the system.
