Easiest way to serve different content from the same link based of user agent

I am current using an Amazon EC2 server to perform a GET on a url that comes in, read the ID in the the url (?id=XXXXX) and display and image based on the ID.

I then read the user agent and if it's mobile display one image, if it's desktop display another image. This could also be split as android vs iphone, or other parameters.

My question is, is there another way other than a EC2 server to do this? Is it possible to do this with a CDN that can pick the appropriate file?