title: GitLab runner docker executor calls back gitlab server by IP address
body: <p>I have private GitLab server running in the cloud (bitnami image). I have a custom domain registered with the public IP of Gitlab Server and letsencrypt certificate generated for this domain. I can access gitlab server by <a href="https://mycustomdomain/" rel="nofollow noreferrer">https://mycustomdomain/</a>.
  I have installed gitlab-runner on linux host and successfully registered (docker executor) with gitlab server (<a href="https://mycustomdomain/" rel="nofollow noreferrer">https://mycustomdomain/</a>). </p>
  
  <p>Now when i then run the pipeline, it fails with following message:</p>
  
  <pre><code>Pulling docker image node:latest ...
  Using docker image sha256:2a0d8959c8e1b967d926059e555fdd23926c8fff809a0cf5fab373e694bbce64 for node:latest ...
  Running on runner-PcudM7CB-project-1-concurrent-0 via my-gitlab-worker...
  Fetching changes with git depth set to 50...
  Initialized empty Git repository in /builds/root/microcities/.git/
  Created fresh repository.
  fatal: unable to access 'https://&lt;my gitlab public IP&gt;/root/microcities.git/': SSL: no alternative certificate subject name matches target host name 'my gitlab public IP'
  ERROR: Job failed: exit code 1
  </code></pre>
  
  <p><strong>Why does the runner/docker container refer to gitlab server by it's IP rather than by domain name?</strong></p>