title: GitLab Runner & Docker: ERROR: Preparation failed: Error: No such image
body: <p>When attempting to pull public images (e.g. <code>python:3.6</code>, <code>node:latest</code>) from Docker, our GitLab runner failed with the following error message:</p>
  <pre><code>Running with gitlab-runner 12.2.0 (a987417a)
    on GitLab Runner XYZ
  Using Docker executor with image python:3.6 ... 00:17
  Starting service python:3.6 ...
  Pulling docker image python:3.6 ...
  ERROR: Preparation failed: Error: No such image: python:3.6 (executor_docker.go:199:0s)
  </code></pre>