title: disable default authentication in mongo docker
body: <p>I want to disable the default auth
  (avoid to use mongo --authenticationDatabase "auth_db").</p>
  
  <p>in mongo using docker-compose, here is my <strong>docker-compose</strong> file:</p>
  
  <pre><code>version: "2"
  
  services:
      mongodb:
      image: mongo:latest
      environment: 
        - MONGO_DATA_DIR=/data/db
        - MONGO_LOG_DIR=/dev/null
        - MONGO_INITDB_ROOT_USERNAME=some_user
        - MONGO_INITDB_ROOT_PASSWORD=some_password
      volumes:
        - ./mongo_data:/data/db
      ports:
        - 27017:27017 
  </code></pre>