Question : Best Practice DNS setup for failover or round robin

We are hosting a website on a server that has two global IPs assigned to it on the same server. Each IP originates from a different ISP. The first IP is the primary IP we'd like the site to respond on, and so our current A record for www is pointing here. The 2nd IP, is for our backup ISP, which we prefer not to use except if the first IP is down.

What type of setup do we need to configure on our DNS server such that, without delay, if a visitor is unable to call up the website on the primary IP, the 2nd IP is returned from their DNS lookup and they would continue to the website via that route instead. Ideally, we'd like this transition to occur automatically and without delay for any customer, regardless of whether or not their DNS server has cached our record.

Do we need to setup a Round Robin DNS?
If so, how or what determines if the 2nd IP is returned? Does it behave like a failover, or does it behave as if it's load balanced? If the first is down, does the 2nd work automatically and without delay?

Thank you!

Answer : Best Practice DNS setup for failover or round robin

It's likely to only effect customers that are actively using the site at the moment, because with a short TTL (Time To Live) they're the only ones who will have a copy of the record in memory.

Chris