Busy web-sites often use multiple web-servers in order to handle traffic
Traffic can be distributed (load balanced) between such web-servers using DNS
The DNS server simply rotaates the DNS records for each incoming DNS request,
resulting in each visitor being served by a different web-server.
However, DNS round robin in itself does not provide any failover functionality.
If one of the web-servers fail, some visitors will still be directed to the
Simple Failover can correct this situation by removing the failed web-server
from the DNS round robin set: