The web is littered with millions of links which previously worked but no longer do. When users encounter any such broken link, they resort to looking up an archived copy of the linked page. But, for a sizeable fraction of these broken links, no archived copies exist. Even if a copy exists, it often poorly approximates the original page, e.g., any functionality on the page which requires the client browser to communicate with the page's backend servers will not work, and even the latest copy will be missing updates made to the page's content after that copy was captured.

Content delivery networks (CDNs) provide fast service to clients by replicating content at geographically distributed sites. Most CDNs route clients to a particular site using anycast or unicast with DNS-based redirection. We analyze anycast and unicast and explain why neither of them provides both precise control of user-to-site mapping and high availability in the face of failures, two fundamental goals of CDNs. Anycast compromises control (and hence performance), and unicast compromises availability. We then present new hybrid techniques and demonstrate via experiments on the real Internet that these techniques provide both a high level of traffic control and fast failover following site failures.