Docker ports are not exposed

Question

I set up a simple node server in Docker.

Dockerfile

FROM node:latest
RUN apt-get -y update
ADD example.js .
EXPOSE 1337   
CMD node example.js

example.js

var http = require('http');
http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello World\n'+new Date);
}).listen(1337, '127.0.0.1');
console.log('Server running at http://127.0.0.1:1337/');

Now build the image

$ docker build -t node_server .

Now run in container

$ docker run -p 1337:1337 -d node_server  
$ 5909e87302ab7520884060437e19ef543ffafc568419c04630abffe6ff731f70

Verify the container is running and ports are mapped:

$ docker ps  

CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                    NAMES
5909e87302ab        node_server         "/bin/sh -c 'node exa"   7 seconds ago       Up 6 seconds        0.0.0.0:1337->1337/tcp   grave_goldberg

Now let's attach to the container and verify the server is running inside:

$ docker exec -it 5909e87302ab7520884060437e19ef543ffafc568419c04630abffe6ff731f70 /bin/bash 

And in the container command line type:

root@5909e87302ab:/# curl http://localhost:1337
Hello World
Mon Feb 15 2016 16:28:38 GMT+0000 (UTC)

Looks good right?

The problem

When I execute the same curl command on the host (or navigate with my browser to http://localhost:1337) I see nothing.

Any idea why the port mapping between container and host doesn't work?

Things I already tried:

• Running with the --expose 1337 flag

Answer 1

Your ports are being exposed correctly but your server is listening to connections on 127.0.0.1 inside your container:

http.createServer(function (req, res) {
    res.writeHead(200, {'Content-Type': 'text/plain'});
    res.end('Hello World\n'+new Date);
}).listen(1337, '127.0.0.1');

You need to run your server like this:

http.createServer(function (req, res) {
    res.writeHead(200, {'Content-Type': 'text/plain'});
    res.end('Hello World\n'+new Date);
}).listen(1337, '0.0.0.0');

Note the 0.0.0.0 instead of 127.0.0.1.