title: gitlab CI : Error loading key : invalid format
body: <p>I'm stuck with this problem since 2 days.</p>
  
  <p>Tried with id_rsa.pub and id_rsa from my production server, still the same error...
  SSH_PRIVATE_KEY is a variable I created in the CI/CD Settings on GitLab.</p>
  
  <p>edit : not protected, not masked.</p>
  
  <pre><code># This file is a template, and might need editing before it works on your project.
  # Official framework image. Look for the different tagged releases at:
  # https://hub.docker.com/r/library/node/tags/
  image: node:alpine
  
  stages:
    - deploy
  
  deploy:
    stage: deploy
    before_script:
      # Install ssh-agent if not already installed, it is required by Docker.
      # (change apt-get to yum if you use a CentOS-based image)
      - 'which ssh-agent || ( apk add --update openssh )'
  
      # Add bash
      - apk add --update bash
  
      # Add git
      - apk add --update git
  
      # Run ssh-agent (inside the build environment)
      - eval $(ssh-agent -s)
  
      # Add the SSH key stored in SSH_PRIVATE_KEY variable to the agent store
      - echo "$SSH_PRIVATE_KEY"
      - echo "$SSH_PRIVATE_KEY" | ssh-add -
  
      # For Docker builds disable host key checking. Be aware that by adding that
      # you are suspectible to man-in-the-middle attacks.
      # WARNING: Use this only with the Docker executor, if you use it with shell
      # you will overwrite your user's SSH config.
      - mkdir -p ~/.ssh
      - '[[ -f /.dockerenv ]] &amp;&amp; echo -e "Host *\n\tStrictHostKeyChecking no\n\n" &gt; ~/.ssh/config'
      # In order to properly check the server's host key, assuming you created the
      # SSH_SERVER_HOSTKEYS variable previously, uncomment the following two lines
      # instead.
      # - mkdir -p ~/.ssh
      # - '[[ -f /.dockerenv ]] &amp;&amp; echo "$SSH_SERVER_HOSTKEYS" &gt; ~/.ssh/known_hosts'
    script:
    - npm i -g pm2
    - pm2 deploy ecosystem.config.js production
    only:
    - master
  </code></pre>
  
  <p>And when I run the pipeline, I still get this error...</p>
  
  <pre><code>$ echo "$SSH_PRIVATE_KEY" | ssh-add -
  Error loading key "(stdin)": invalid format
  </code></pre>
  
  <p>Could you please help ? I'm helpless, clueless, hopeless loading...</p>
  
  <p>Thanks very much !</p>