This is the latest in a series of DNS articles that I've been writing over the past couple of months.  This article is taken from a fantastic solution that Joe Cassidy developed.  So, thanks to Joe for developing this solution, and thanks for the opportunity to write about it here on DevCentral.  As a quick reminder, my first six articles are:

  1. Let's Talk DNS on DevCentral
  2. DNS The F5 Way: A Paradigm Shift
  3. DNS Express and Zone Transfers
  4. The BIG-IP GTM: Configuring DNSSEC
  5. DNS on the BIG-IP: IPv6 to IPv4 Translation
  6. DNS Caching


The Scenario

Let's say you are an F5 customer who has external GTMs and LTMs in your environment, but you are not leveraging them for your main website (  Your website is a zone sitting on your windows DNS servers in your DMZ that round robin load balance to some backend webservers. 

You've heard all about the benefits of the cloud (and rightfully so), and you want to move your web content to the Amazon Cloud.  Nice choice!  As you were making the move to Amazon, you were given instructions by Amazon to just CNAME your domain to two unique Amazon Elastic Load Balanced (ELB) domains.  Amazon’s requests were not feasible for a few of which is that it breaks the RFC.  So, you engage in a series of architecture meetings to figure all this stuff out. 

Amazon told your Active Directory/DNS team to CNAME and to two AWS clusters: and  You couldn't use Microsoft DNS to perform a basic CNAME of these records because of the BIND limitation of CNAME'ing a single A record to multiple aliases.  Additionally, you couldn't point to IPs because Amazon said they will be using dynamic IPs for your platform.  So, what to do, right?


The Solution

The good news is that you can use the functionality and flexibility of your F5 technology to easily solve this problem.  Here are a few steps that will guide you through this specific scenario:

  • Redirect requests for to and apply it to your Virtual Server (  You can redirect using HTTP Class profiles (v11.3 and prior) or using a policy with Centralized Policy Matching (v11.4 and newer) or you can always write an iRule to redirect!


  • Make a CNAME record to; where * is a sub-delegated zone of that resides on your BIG-IP GTM.


  • Create a global traffic pool “aws_us_east” that contains no members but rather a CNAME to
  • Create another global traffic pool “aws_us_west” that contains no members but rather a CNAME to 

The following screenshot shows the details of creating the global traffic pools (using v11.5).  Notice you have to select the "Advanced" configuration to add the CNAME.


GSLB Pool Create




  • Create a global traffic Wide IP with two pool members “aws_us_east” and “aws_us_west”.  The following screenshot shows the details.


WIP Pool Members




  • Create two global traffic regions: “eastern” and “western”.  The screenshot below shows the details of creating the traffic regions.


Region Create



  • Create global traffic topology records using "Request Source: Region is eastern" and "Destination Pool is aws_us_east".  Repeat this for the western region using the aws_us_west pool.  The screenshot below shows the details of creating these records.


Record Create




  • Modify Pool settings under Wide IP to use "Topology" as load balancing method.  See the screenshot below for details.

WIP Load Balance



How it all works...

Here's the flow of events that take place as a user types in the web address and ultimately receives the correct IP address.


  • External client types into their web browser


  • Internet DNS resolution takes place and maps to your Virtual Server address:  IN A


  • An HTTP request is directed to


  • Your LTM checks for a profile, the HTTP profile is enabled, the redirect request is applied, and redirect user request with 301 response code is executed


  • External client receives 301 response code and their browser makes a new request to


  • Internet DNS resolution takes place and maps to IN CNAME


  • Internet DNS resolution continues mapping to your GTM configured Wide IP


  • The Wide IP load balances the request to one of the pools based on the configured logic:  Round Robin, Global Availability, Topology or Ratio (we chose "Topology" for our solution)


  • The GTM-configured pool contains a CNAME to either us_east or us_west AWS data centers


  • Internet DNS resolution takes place mapping the request to the ELB hostname (i.e. and gives two A records


  • External client http request is mapped to one of the returned IP addresses



And, there you have it.  With this solution, you can integrate AWS using your existing LTM and GTM technology!  I hope this helps, and I hope you can implement this and other solutions using all the flexibility and power of your F5 technology.