title: Why do some Docker images have no VOLUME defined?
body: <p>I am just starting with Docker, please pardon me if my question is too silly for you.</p>
  
  <p>I see some images, like <code>nginx</code>, does not have any <code>VOLUME</code> defined whereas some images like <code>mysql</code> has <code>VOLUME</code> defined in their Dockerfile.</p>
  
  <p>How the data or files are managed when there is no volume defined, and what would be their working directory?</p>