AWS News Blog

Moving Ahead With Amazon Route 53

As you may know from my previous post, Amazon Route 53 is a highly available and highly scalable DNS service.

Today we have some big news for users and fans of Route 53:

  • You can use a new alias feature to map the root or apex of your hosted zone to your Elastic Load Balancer.
  • Route 53 is now considered Generally Available, and now has a Service Level Agreement, or SLA.
  • You can now provide multiple answers to a single DNS question using a Weighted Round Robin model.

Aliases and the Zone Apex
A number of our customers use an Elastic Load Balancer in front of a fleet of EC2 instances. The EC2 instances host the web tier of their application. Unfortunately, due to the way that the DNS protocol works, there was no way to refer to the Elastic Load Balancer from the root (also known as the apex) of the domain. In Plain English, you could create a DNS entry that maps to an Elastic Load Balancer but you couldn’t do the same for

Because short, memorable URLs are always desirable, we’ve created a new aliasing system for Route 53. You can now map the apex of a hosted zone to an Elastic Load Balancer using an Alias record. When Route 53 encounters an Alias record, it looks up the A records associated with the target DNS name in the Alias, and returns the IP addresses from that name.

The DNS entries associated with an Elastic Load Balancer have a short (60 second) time to live, or TTL. This means that changes to the entries will be recognized and respected as quickly as possible. In order to allow all of our customers to benefit from this new feature, there is no charge for queries to alias records when the target is an Elastic Load Balancer (the only allowable target in this release).

General Availability and SLA
We launched Route 53 in beta form in December of 2010. Developers all over the world have eagerly adopted Route 53 and it now provides DNS services for a multitude of websites. The service is now officially generally available. The Route 53 Service Level Agreement offers 100% availability (measured at 5 minute intervals) and provides service credits as follows:

  • A one day credit for 5-30 minutes of unavailability.
  • A one week credit for 31 minutes to 4 hours of unavailability.
  • A one month credit for more than 4 hours of unavailability.

Weighted Round Robin
A primary task of a DNS service like Route 53 is to answer the question “What is the IP address associated with this name?” You can now provide multiple answers for a name, and you can also control the relative frequency with which each one is used. This model is called Weighted Round Robin (WRR) DNS. You can use this new feature to implement a variety of different scenarios. For example, you could route different amounts of traffic to EC2 instances with varied amounts of processing power. Or, you could do some A/B or functional testing.

You can learn more about aliasing and WRR in the Route 53 documentation.

— Jeff;

Jeff Barr

Jeff Barr

Jeff Barr is Chief Evangelist for AWS. He started this blog in 2004 and has been writing posts just about non-stop ever since.