title: I can't use a specific port with a docker container
body: <p>I don't manage to make the <code>docker-compose up</code> work.</p>
  <p>When I enter it, I immediately get those errors :</p>
  <pre><code>Starting test_application_1 ... 
  Starting test_application_1 ... error
  
  ERROR: for test_application_1  Cannot start service application: Ports are not available: exposing port TCP 0.0.0.0:5000 -&gt; 0.0.0.0:0: listen tcp 0.0.0.0:5000: bind: address already in use
  
  ERROR: for application  Cannot start service application: Ports are not available: exposing port TCP 0.0.0.0:5000 -&gt; 0.0.0.0:0: listen tcp 0.0.0.0:5000: bind: address already in use
  ERROR: Encountered errors while bringing up the project.
  </code></pre>
  <p>So I used <code>netstat</code> (I typed <code>netstat -av | grep 5000</code> on the MacOS terminal) to see if the 5000 port was used but the command doesn't display it so I don't think it's actually used...</p>
  <p>Here is the content of the <code>docker-compose.yml</code> file :</p>
  <p>version: &quot;3&quot;
  services:
  redis:
  image: redis
  application:
  image: some_application
  ports:
  - 5000:5000</p>
  <p>The image <code>some_application</code> is from an exercise.</p>
  <p>Anyone knows what is happening and how to fix this problem ?</p>
  <p>Thx !</p>