Gitlab Registry port and host clarification

I spend a lot of time to understand why I cannot contact to the Gitlab Registry (defined by $GITLAB_REGISTRY_HOST:$GITLAB_REGISTRY_PORT). I did not defined SSL_REGISTRY_CERT_PATH and SSL_REGISTRY_KEY_PATH, because I'm running behind an external proxy which handle HTTPS.
So in this case, you only have to proxy to the Docker Registry (port 5000, from the registry:2 docker image), and so the GITLAB_REGISTRY_HOST and GITLAB_REGISTRY_PORT is only here to inform the gitlab users what is the Docker Registry domain..

I thing this should be mentioned somewhere, like "You can connect to the Docker Registry directly if you handle SSL yourself, and so these param only define the Docker Registry endpoint in the registry tab of a Gitlab project. When you will try to connect to the Docker Registry, it will tell your docker to connect to the Gitlab JWT auth service to get authenticated".

Actualy, even the Gitlab offical doc is very confuse : does Gitlab have it own Registry-app which is proxy the Docker Registry ? No : it's just a simple proxy defined in nginx.
So there is no difference between docker login registry.gitlab.example.com and docker login registry:5000 except that you expect to have SSL enabled on registry.gitlab.example.com (because proxied by nginx with ssl).

In fact there is no difference with the schema of the offical doc except this nginx proxy to add SSL over the registry.
And so you could even set the domain name of the registry as the same as the gitlab domain (gitlab.example.com) if you handle correctly the request in your proxy (for example by detecting ^/v2 in the request, or/and the docker user-agent string).

Start by reviewing the documented GitLab Registry environment variables and the referenced assets/runtime/config/nginx/gitlab-registry file. Compare the Docker Registry authentication flow with the nginx proxy setup described in the issue. Done means the documentation clearly explains the registry endpoint, port 5000, external SSL termination, and JWT authentication relationship.