CumulonimbusHi,
 
I found this article too late... I wrote my own code before :-( ! The picture made me laugh because it remembered me trying to understand the DNS encoding logic in RFC..
 
I had a customer who used the DNS-Lite license for DC HA requirements for only one Application : Exchange.
 
there are only 4 DNS servers requesting to this record.
 
The rate limite of this license was enough for this need. There is 1 dns request per minute for the only one record.
 
Now the customer had to upgrade to 12.1.2 Appliances so I had to find a solution before to reactivate the license. the DNS license is too expensive for this little need.
 
I first wrote an irule like yours which worked when I requested from dig and nslookup utility to the F5 but I have encountered an issue when the DNS server includes a "additional record".
 
This record is appended after the question, so it is included in the ${question} variable. As you insert the answer after it, there is a mismatch in the response.
 
the customer's AD 2012 always included an additional record. so the answer was rejected and the DNS cache was cleared... Exchange was not working anymore. oops!
 
You can look at my code DNS lite with topology selection witch decode the request and encode the response based on pool member availability.