DevDock todo

Imagine this typo:

    volumes:
      - ${dd_dirr}'/etc/ssh:/ssh-config'
    command: ['head', '-n', '2', '--', '/ssh-config/ssh_host_rsa_key']

Thus: Make ${DD:dirr} (empty variable) a syntax error

Research todo

Docker-compose configs feature: https://docs.docker.com/compose/compose-file/05-services/#configs https://docs.docker.com/compose/compose-file/08-configs/