I have my static website hosted on bigrock.com.. (xyz.com). I recently created a webapp which I am hosting on Amazon AWS. I wanted my subdomain sub.xyz.com to be redirected to the app deployed on AWS.I created a subdomain in bigrock and redirected the same to the URL of the EC2 instance in AWS. When I did that when I access sub.xyz.com the URL in the browser changes and I get redirected to the amazon app. How do I hide the EC2 URL and have the user operate out of sub.xyz.com. Also, when I do this, any other URLs like sub.xyz.com/something or sub.xyz.com?something=somethingelse should also work. Could you please tell me what I need to do on the CPanel of bigrock to make this happen? 
Forward subdomain to a new URL but retain the URL entered by the user - Bigrock
cpanel;cname;domain forwarding
Did Amazon AWS provide you with the IP address for your server where you have hosted your application? If yes, you can try adding an A record for the sub-domain and point it to that IP address.