2 IPs 1 Cup

[Madman]

Actually, 2 IPs 1 domain techincally. I was going to go ask my IT department, but this is much easier and I won't get looked at funny.

I'm looking how to have one domain, but 2 separate IPs to have fault tolerance between 2 servers.

I want one server to be the primary server and where everyone is directed to first when they hit the domain name. In the event that the first IP is unreachable, then the user would be directed to the second IP.

I've read about "round robin" dns stuff, but I don't want the second server to be used unless absolutely necessary as co-location bandwidth overage charges are not something we like to pay for if we don't have to.

Is there a DNS service out there that can do something like this? How about one that is smart enough to take the primary IP offline automatically, or for a certain period of time if it isn't responding?

Any help would be appreciated.

[sclitheroe]

You could load balance them with priorities configured, that is pretty easy to set up on Windows 2003/2008, and pretty simple on Linux too I would imagine. This isn't an ideal configuration, because if the primary server is up, but web services are down, WLBS will continue to direct traffic to it.

A purely DNS solution isn't ideal for internet facing servers, as DNS caching upstream is going to cause issues, I would think, unless you run your own DNS server and want to handle the additional traffic of constant lookups using non-cacheable entries. I'm not sure how widely supported a TTL of 0 at any rate.

[Madman]

The servers are at two different locations and the second server's purpose in life is to act strictly as a backup if the main server goes down for any reason - I don't want to load balance them.

[Barnes]

Our IT department will look at you funny regardless.

[photon]

http://support.easydns.com/Failoverfaq.php

DNS changes aren't instant and aren't 100% reliable either; not everyone obeys the ttl. I've read that most providers won't even obey a ttl of less than half an hour I think, so half an hour is kind of the minimum amount of downtime you will see with this kind of solution. Plus having a low ttl means more DNS requests which means more expensive DNS.

So the question is how much downtime is acceptable?

[Madman]

Thanks all, except you Barnes.

Good info to work with.

[photon]

There are other options available if you need much higher uptime. I think there are services that put a proxy load balancer in front of the sites, so the IP doesn't change, but the load balancer will use one or the other depending on what's required (i.e. don't use it to balance, just to do failover).

[Bibtin Tex]

Thread title is misleading

[Phaneuf3]

Originally Posted by photon

There are other options available if you need much higher uptime. I think there are services that put a proxy load balancer in front of the sites, so the IP doesn't change, but the load balancer will use one or the other depending on what's required (i.e. don't use it to balance, just to do failover).

This is the first thing I thought of when I opened the thread.