I'm not sure whether I should post this here or on the Docker repo, but I'll start here.

I'm testing out running a private registry for internal use inside our Amazon VPC. I've got the registry configured on an EC2 instance, with an Elastic Load Balancer (ELB) in front of it.

When I push an image to the registry, it works whether I'm using the ELB address or the actual IP of the EC2 instance:

2014/07/22 17:03:03 POST /images/<my_elb_address>.elb.amazonaws.com/busybox/push?tag=latest
[c8df8586] +job push(<my_elb_address>.elb.amazonaws.com/busybox)
[c8df8586] -job push(<my_elb_address>.elb.amazonaws.com/busybox) = OK (0)

However, when I try to pull the same image out of the registry, using the ELB address fails:

2014/07/22 17:03:44 POST /images/create?fromImage=<my_elb_address>.elb.amazonaws.com%2Fbusybox&tag=
[c8df8586] +job pull<my_elb_address>.elb.amazonaws.com/busybox, )
[error] server.go:1161 Repository not found
Repository not found
[c8df8586] -job pull(<my_elb_address>.elb.amazonaws.com/busybox, ) = ERR (1)

Trying to pull that same image from the registry via the hardcoded IP address works, however:

2014/07/22 17:10:24 POST /images/create?fromImage=<my_ip>%3A5000%2Fbusybox&tag=
[c8df8586] +job pull(<my_ip>:5000/busybox, )
[c8df8586] -job pull(<my_ip>:5000/busybox, ) = OK (0)

So it would seem that something changes between using my ELB and my hardcoded instance IP that causes pulls to not work. Pushes continue to work on both addresses, however.

I'm not sure what other information you'd need to look at this, but does this look like a Docker Registry issue or a Docker daemon issue?