We host one web server on our office internet connection (cheap!). The DNS servers are external and not provided by the ISP.
When the connection goes down we would like to have a backup solution. The basic idea is to get a second internet connection with a different ISP (separate last-mile), and a different IP number.
How would one go about minimizing the downtime for the users of our web site? How far would we get by setting the DNS TTL to perhaps a couple of minutes, and then be ready to switch over to the backup IP number when problems occur (automatically or manually)?