route traffic to global datacenters using DNS

[Glen Wiley]

On Feb 24, 1:29 am, stevehunte... at hotmail.com wrote:
> Scenario:
> 2 Datacenters at two different geographic regions.
> Each datacenter has its own set of DNS servers (lets say 2)
>
> If I assign nameservers to a domain name in the following order:
> location1A
> location1B
> location2A
> location2B
>
> For "failover", it would be logical that the DNS for location1A would
> point to servers at location#1.  So if location#1 failed, DNS servers
> 1A and 1B would be down, and DNS servers for 2A and 2B would pick up
> the traffic and they would route to servers at location#2.
>
> This is all fine and with a TTL of one minute would work very well.
> But what if I wanted to load balance (round robin) to location1 and
> location2?
>
> So location1A DNS server would round robin to location1 and
> location2.  What happens when location2 goes down, how do you fix
> this?  Because location1A DNS is still going to hand our location#2 IP
> addresses ...  what are the real-world examples?  manually changing
> the DNS is a solution, but not a fast solution.  What tools or
> techniques are people using?  I am sure this has been addressed before
> but I could not find any information on it.
>
> So the requirement I have is to load balance (round robin), TTL of a
> minute or less, and to incorporate some type of failover using the
> DNS.
>
> Thanks for any assistance

You should spend some time exploring GSLB - this is a commonly
implemented approach.  You will find some people who argue that "GLSB
does not work", however I would take their comments with a grain of
salt - the realityis that it does work and is used by many of the
largest internet service companies.

GSLB is typically implemented using specialized hardware so it is not
cheap and you will want to make sure that you understand the effect on
your applications.

For a quick explanation of GSLB take a look at:

http://www.networkworld.com/news/tech/2000/0731tech.html

A decent but brief explanation of GSLB including some thoughts about
when and when not to use it is here:

http://blogs.sun.com/davew/category/Networking