Costed A Records? 1

[peterlyttle]

Hello, here is my current problem. I have 2 offices (Office A and Office B) with separate internet connections. The web servers in both offices have the same content for redundancy. Is it possible when I access

http://www.domain.com

that it always goes to Office A unless Office A is unavailable in which case it will go do Office B. Similar to MX records Priority. My domain DNS is managed my ISP and we use their name servers.
Can anyone give me some advice please?

Cheers,
Peter

 

[elgrandeperro]

On paper, this sounds doable, but here is why it might not be.

First, you don't have absolute control of your DNS. You must have the ability to change the ordering of the records and prevent "round robining", where it gives out record A/B then B/A, etc. And you must have the ability to set a low TTL, so that you can switch the order and avoid caching. But if you have these abilities, you might as well just advertise A or B and not both!

But the user experience when the first server is down will not be good. I think (not verified) that if you advertised A/B and A were down, each http request would have to encounter a TCP timeout.

Lastly, even if you could control which server is advertised as "running" with a low TTL, some ISPs disregard the TTL for
caching purposes. So you could make a change, and expect the TTL to correctly propagate across the Internet and realize the change hasn't been progapated %100 even after the TTL should have expired it.

So my take is that DNS isn't the way to get this to work.

egp