title: How to expose ports only within the docker network?
body: <p>I have a few apps running in a Docker network with their ports (<code>3000</code>,<code>4200</code>, etc) exposed. I also have an nginx container running within the same Docker network which hosts these apps on port <code>80</code> with different domain names (<code>site1.com</code>, <code>site2.com</code>).</p>
  
  <p>But right now if I go directly to the ports the apps are running on (<code>localhost:3000</code>) I can access them that way too. </p>
  
  <p>How do I expose those ports only to the nginx container and not the host system?</p>