GitLab cannot be hosted on a domain

Hello, GitLab community!

I just installed GitLab with the official Docker image provided (https://hub.docker.com/r/gitlab/gitlab-ce). Everything went smoothly. I managed to change the external_url parameter (external_url 'gitlab.example.com', was that correct?) and did gitlab-ctl reconfigure. I’m a bit surprised that GitLab is so easy to set up (I expected some problems, hearing what other people said). But the problem came straight when I tried to access GitLab through my domain.

I’m using caddy (reverse proxy) to redirect all my traffic from the domain to the Docker container (127.0.0.1:8002, as written). However, when I tried to access the domain, it redirected me to 127.0.0.1:8002, which will be a trouble for people accessing from outside the network, right?

I’ve done some searching and the closest I got to is this in the GitLab docs.

Can anyone tell me how to stop GitLab from redirecting to a non-domain address? Thanks!