High Availability

From DesigningPatterns

• Building Scalable Web Sites is an excellent book on the subject (it devotes a chapter to it).

There are a number of DNS failover vendors (search for "dns service failover"):

• AutoFailover offers quick (under three minutes) service for about $100 / month.
• ZoneEdit
• UltraDNS
• DNSMadeEasy is another DNS failover vendor ($50 / month).
• Netriplex seems to have impressive explanations and offers a variety of pricing plans.
• DynDNS offers Dynect.

Round-robin DNS failover will cause the browser to wait for about 20 seconds for each down IP address. One can write or download a script to poll one's servers and failover in case of failure.