DNS Disaster Recovery - How to Easily Update DNS When Server Goes Down

[howecc]

I have a web server with about 20 websites and worry about what will happen if the server goes down. If the server fails and I need to restore an image to another server with a differnt IP address, how can I quickly reset the DNS "A" records to use the new IP address of the new server (I do have access to each domain registrar to change the DNS "A" record).

Can I enter multiple "A" records and it will failover to the second server (I do not want any traffic to the second server unless the first server is down)? Is there an intermediary DNS server that can help?

 

[Ijack]

In such a situation I would either change the address of the second server to match that of the first or else create a second address to achieve this.

Because of DNS caching it can take a matter of hours (or more) for DNS changes to propogate through all DNS servers. Presumably you want your web sites to be available as soon as possible; using the same IP address achieves this.

This assumes that you have access to the server and can make these changes.