Rootless edge-case: defaults to http when registry resolves to 127.0.0.1

[desnij]

Debian buster: Docker version 20.10.16, build aa7e414

Background

On a vanilla debian system

1. As root everything works as expected, including our in-house repo
2. Using rootless as a user "ubuntu", "gcr.io/myproject/alpine" etc all work
3. but the in-house registry fails as seen below.

• this happens when the host resolves to 127.0.0.1 ( in my case, due to the use of ssh tunnels)
• it happens regardless of what port is used.

$ docker pull reg.my.domain:443/alpine
Using default tag: latest
Error response from daemon: Get "http://reg.my.domain:443/v2/": dial tcp 127.0.0.1:443: connect: connection refused

Failed attempt at a work around.

I tried to tunnel the registry to the host ip ( ssh -L 0.0.0.0:443:reg.my.domain:443 myjumppoint ) but that fails because now docker wants to resolve the dns rather than read /etc/hosts as done when the ip is 127.0.0.1.

$ docker pull  reg.my.domain:443/alpine
Using default tag: latest
Error response from daemon: Get "https://reg.my.domain:443/v2/": dial tcp: lookup reg.my.domain on 10.0.2.3:53: server misbehaving

Edge-case notes

1. docker defaults to http when using a reg on 127/8
2. docker requires dns when host is not 127.0.0.1 ( this may virtualbox related )

[desnij]

moving this to docker/cli