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DNS Round Robin Configuration. June 21, 2010

If you are hosting a popular site, you will face a problem in which your server simply can’t serve any more requests.

In the web server world, this is called the Slashdot effect.

One way to overcome the limits of the monolithic server is to distribute the load across many machines. By adding a second (or third) server to the available pool of machines, you can not only increase performance but also add to the stability of the network. If you have a hot spare (or three) running all of the time, then if one develops trouble, the others can take over for it without any downtime.

The easiest way to distribute the load of public traffic is to use the magic of round-robin DNS, inbound requests to a single host name can be directed to come from any number of IP addresses.

We use this in the zone file for our network zone “networknuts.net”:

www 60 IN A 172.24.0.254
www 60 IN A 172.24.0.111

Now, when a hosts looks up www.networknuts.net in DNS, about half of the time they will see:

$ host www.networknuts.net

http://www.networknuts.net has address 172.24.0.254
http://www.networknuts.net has address 172.24.0.111

(172.24.0.254 and 172.24.0.111 are my name-servers hosting http://www.networknuts.net)

and the rest of the time, they get:

$ host www.networknuts.net

http://www.networknuts.net has address 172.24.0.111
http://www.networknuts.net has address 172.24.0.254

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God Bless.