Exposing a port on a live Docker container

Question

I'm trying to create a Docker container that acts like a full-on virtual machine. I know I can use the EXPOSE instruction inside a Dockerfile to expose a port, and I can use the -p flag with docker run to assign ports, but once a container is actually running, is there a command to open/map additional ports live?

For example, let's say I have a Docker container that is running sshd. Someone else using the container ssh's in and installs httpd. Is there a way to expose port 80 on the container and map it to port 8080 on the host, so that people can visit the web server running in the container, without restarting it?

Answer 1

Here's another idea. Use SSH to do the port forwarding; this has the benefit of also working in OS X (and probably Windows) when your Docker host is a VM.

docker exec -it <containterid> ssh -R5432:localhost:5432 <user>@<hostip>

Answer 2

You can use SSH to create a tunnel and expose your container in your host.

You can do it in both ways, from container to host and from host to container. But you need a SSH tool like OpenSSH in both (client in one and server in another).

For example, in the container, you can do

$ yum install -y openssh openssh-server.x86_64
service sshd restart
Stopping sshd:                                             [FAILED]
Generating SSH2 RSA host key:                              [  OK  ]
Generating SSH1 RSA host key:                              [  OK  ]
Generating SSH2 DSA host key:                              [  OK  ]
Starting sshd:                                             [  OK  ]
$ passwd # You need to set a root password..

You can find the container IP address from this line (in the container):

$ ifconfig eth0 | grep "inet addr" | sed 's/^[^:]*:\([^ ]*\).*/\1/g'
172.17.0.2

Then in the host, you can just do:

sudo ssh -NfL 80:0.0.0.0:80 root@172.17.0.2