title: Docker named volume not updating
body: <p>I am confused on how the named data-volume (not data container) should be used.</p>
  
  <p>I have a named data volume <code>app_src</code> that is mounted to <code>/usr/src/app</code> using docker compose file. However, after making changes to my source code (locally), building the image doesn't update the volume.</p>
  
  <p>I am building the image like so,</p>
  
  <p><code>docker-compose -f development.yml build</code> and running it <code>docker-compose -f development.yml up -d</code>.</p>
  
  <p>To confirm that the volume doesn't change, I attached into the running container and true enough, the source code isn't updated.</p>
  
  <p>Here is my docker compose file <code>development.yml</code> and <code>Dockerfile</code> for my <code>web</code> service.
  version: '2'</p>
  
  <pre><code>services:
    web:
      restart: always
      build: ./web
      expose:
        - "8000"
      volumes:
        - app_src:/usr/src/app
      links:
        - postgres:postgres
      env_file: development.env
      command: ./start_web.sh
  
  volumes:
     app_src: {}
  
  
  FROM python:3.4.4
  
  WORKDIR /usr/src/app
  RUN rm -rf /usr/src/app/*
  COPY . /usr/src/app/
  RUN pip install --no-cache-dir -r requirements.txt
  </code></pre>
  
  <p>I could make it work by mounting the host like so,</p>
  
  <pre><code>volumes:
      - ./web/src:/usr/src/app
  </code></pre>
  
  <p>I'm on Ubuntu 16.04 running docker 1.11.2. Is my understanding wrong? I did take a look at the documentation but I could find anything that explained the volume really well.</p>