[donmcronald]

Does it actually send the URL? I think it uses the URL to make the network request, but doesn’t actually send the URL to the registry. If it did, you could use an alternate registry as a pull through cache and have it go upstream for everything. AFAIK that’s not possible.

[TheDong]

Docker's registry protocol is surprisingly complicated. It is stateful, it is not trivially cacheable, and it's a right pain in the ass to deal with