I have an ubuntu server running on Amazon EC2. I want to set my subdomain to serve from this instance.
I have assigned an Elastic IP to the instance. From my domain provider I have forwarded this subdomain to the Elastic IP of the ubuntu instance.
When I try to open my website using my subdomain it is served from the IP instead of the subdomain.
You should setup an "A" record for the subdomain and point it to the elastic IP. You may have created a CNAME and pointed it to the IP instead.