title: Docker port localhost:80 is always listened on
body: <p>I am just studying the Docker and found out it seems that we don't need to run docker-tutorial image and the port:80 is always listened on just like below picture:
  <a href="https://i.stack.imgur.com/wRldx.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wRldx.png" alt="docker tutorial" /></a></p>
  <p>At first, I thought it is automatically managed by Docker Desktop. But it is not. Because after I close the Docker desktop completely, it is still there.
  I even run a command to check the process of port 80 and no process is there:
  <a href="https://i.stack.imgur.com/nO4FS.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nO4FS.png" alt="check port 80" /></a>
  when no process is on this port, it is still running. It drives me crazy. I do have followed docker start tutorial to run this tutorial web application and at that time I can also open localhost:80.
  After that, I have stopped and removed container and even the image as well as closing the Docker app, the page, however, is still there.
  Does any have encountered this situation or have any idea? How does Docker do this?</p>
  <p>After a day, i start my mac again without running Docker and it is still there in a messy way:
  <a href="https://i.stack.imgur.com/AUia4.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/AUia4.png" alt="messy one" /></a></p>