Background : I have a domain, lets say example.com. I assign an elastic IP to a instance on EC2 and give it the dns name as example.com
I want to put 5 instances of EC2 under this domain, like so :
i1.example.com, i2.example.com,...

Question :

1 - is the above said possible ?
2 - if yes how to achieve it ? if no, whats the work around ?



Yes, it is possible.

For the single "example.com" server, you must use an elastic IP and assign the A record of example.com to that IP. This is due to the "zone apex" issue. https://forums.aws.amazon.com/thread.jspa?threadID=32044

For all other sub-domains, I recommend you use a CNAME from "i1.example.com" to the EC2-assigned domain name (e.g. "ec2-AA-BB-CC-DD.compute-1.amazonaws.com"). This method has two benefits:

  1. You do not exhaust your limit on elastic IPs http://aws.amazon.com/ec2/faqs/#Why_am_I_limited_to_5_Elastic_IP_addresses

  2. When referring to these systems, AWS EC2 DNS servers always report the correct IP - if it is being referenced externally it gives the external IP and if being used inside the EC2 cloud it gives the internal IP (no additional bandwidth cost)

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  • Thanks for saying "it is possible" :) And +1 for the links And "Accepted" for the instructions on how to achieve it :) – Shrinath Feb 17 '11 at 7:25

The easiest way is to use the other 4 elastic IPs and apply them to the i-N instances, in which case they'll just be additional DNS entries for those other IPs in your public DNS---no different from www.example.com.

A slightly less ugly version (but much more involved) method would be to run a reverse proxy that looks at the requests coming in and forwards them to the internal addresses of the i-N.example.com instances based on something identifiable at the application layer (e.g. HTTP vhost)

An uglier version would involve procuring a hosted + dynamic DNS service for example.com, and writing a startup script that would update the DNS for the i-N instances appropriately.

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  • when "5" becomes "N", then we've a problem... we cant buy all the elastic ips in the Amazon farm, no ? :D – Shrinath Feb 16 '11 at 6:19
  • Hence the proxy and DDNS alternatives :-P – James Cape Feb 16 '11 at 12:49

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