title: Why can't I access open HTTP port of NiFi flow via Docker?
body: <p>I'm trying to do something very simple:  use the official NiFi docker image (<a href="https://hub.docker.com/r/apache/nifi/" rel="nofollow noreferrer">https://hub.docker.com/r/apache/nifi/</a>) to run a very simple NiFi "Hello World" tutorial (<a href="https://github.com/drnice/NifiHelloWorld" rel="nofollow noreferrer">https://github.com/drnice/NifiHelloWorld</a>).</p>
  
  <p>The problem is that I cannot access the port of the HandleHttpRequest processor from that tutorial (called Nifi-WebServer-HandleHTTP).  The port is 6688.</p>
  
  <p>I've mapped port 6688 to localhost, which I've confirmed in portainer:
  <a href="https://i.stack.imgur.com/7AcBr.png" rel="nofollow noreferrer">Portainer Snapshot Showing port mappings</a></p>
  
  <p>The URL localhost:8080 works fine, I can access the NiFi UI and interact with it.</p>
  
  <p>But when I try localhost:6688, I get an error (empty response from server).</p>
  
  <p><strong>More info</strong></p>
  
  <p>1)  When I log in through Portainer to the "nifi3" container console, I can run "curl localhost:6688", and get the expected result (some HTML coming back).</p>
  
  <p>2)  I've confirmed via netstat that nothing else is using 6688 on my host.</p>
  
  <p>3)  Full container run command:</p>
  
  <pre><code>docker run --name nifi4 -d -p 8080:8080 -p 6688:6688 -p 9998:9998 -v `C:/temp/GitHub/NifiHelloWorld/Archive`:/mnt/nifi_hello_world -v C:/temp/nifi_out:/mnt/nifi_out nifi3 -v 4a8bd6cab08f08af457001810a312816757f40a7c16d2583dd6a9eabfd76db78:/opt/nifi/nifi-current/conf
  </code></pre>
  
  <p>So the HTTP server seems to be up on the correct port inside the container, the port mapping is there, but I cannot access it from outside.</p>
  
  <p>Anyone know why?</p>