[ Thanks to Nobody for this link.
]
“When a Web server’s hostname has more than one A
record, a Web browser will end up being given one IP address from
the list at random. So if you set up two identical servers, about
half of the requests will go to each. This is great for load
balancing, but if one of the servers goes down, then about half of
the requests will be routed to the broken server, and just fail.“However, you may be able to get around that issue by taking
advantage of the fact that DNS servers are required by
specification to fetch all the server IP addresses (stored as NS
records in the DNS), and try them in turn until one succeeds. So if
one server’s down, clients will automatically try another until
they find one that works.”