title: Why docker image doesn't run "docker build"?
body: <p>I'm using gitlab ci, and sorry for the silly question, but why that code below doesn't work?</p>
  <pre><code>image: docker:stable
  
  stages:
    - build
  
  build-docker:
    stage: build
    script:
    - docker build -t my-image .
  </code></pre>
  <p>When I run a docker image of docker on my terminal I'm able to use these commands like <code>docker build</code>.</p>
  <p>For the gitlab-ci above works, I've to add the <code>services: docker:dind</code>, but I don't really understand why, since I've an image that theoretically has the commands that I need.</p>
  <p>Sry about my English, btw.</p>
  <p>Thx in advance.</p>