Load Balancing with DNS Round Robin

You have two web servers with two different IP. These two web servers use the same central storage that contains web code and database. And now, you would like to load balancing those two web servers to serve clients. There are some ways to achieve it, such as establishing a cluster of two web servers, etc. But, the cheapest method could be load balancing hosts using DNS Roud Robin.

This article covers the mechanism of DNS Round Robin and how to configure it. At the end of the article, I also mention about the limit of a new RFC that effects the way DNS Client acts.

Round Robin is a feature that DNS server returns a list of multiple A host records with the same name. Basically, if you want to load balancing your website as www.plaintutorials.net, you need to create 3 A hosts with the same name “www” and point it to different IP addresses, which belongs to your 3 web servers.

DNS Round Robin

When DNS client (web client) queries your DNS server with DNS Round Robin enabled, the DNS server returns the results as a list of 3 IPs. DNS Round Robin randomly rotates the position of those 3 IP of the list, almost 33% the first IP is at the top of the list, and almost 66% the other IPs would be at the top of the list. DNS clients might pick the first IP of the list. I used the word “might” here because there are some exception based on version of clients operating systems.

Steps to configure DNS Round Robin

Enable DNS Round Robin

Round Robin is a feature of DNS Advanced Option. DNS Round Robin is enabled by default at server level on Windows Server. To double check Round Robin feature, follow these steps

  • Start menu, click RUN, and type DNSMgmt.msc to start DNS Management Console
DNS Management Console shortcut
  • Select DNS Server, right click on the server, select Properties
DNS Server Properties
  • Select tab Advanced, make sure Round Robin is checked.
DNS Round Robin option
  • Click OK to close the DNS Server properties dialog.

Next step is to create A host records for those servers you want to load balancing.

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About The Author

Hao Nguyen

Hao Nguyen

Hello! I'm Hao Nguyen and I'm currently working as a Network Engineer for a small firm in Houston. I enjoy writing technical documents and blog, such as PlanTutorials.com

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