They are finding that the waiting time for CacheFly is extremely long. It's as if, each time, the image has to be pulled via Reverse Proxy, but then isn't stored there, as if it's being pulled each time. The problem is probably that your origin header is sending both a set-cookie header, as well as a no-cache header, for your static objects. A solution would be to use Memcached to hold your sessions and turn off session stickiness on ELB.