Open ports to docker container

How to open ports at container launch

Here's the standard way. Let's use port 80 on our local machine to access port 8080 on the docker image. 

$ docker run -d -p 80:8080 springio/gs-spring-boot:latest

And grab the IP addres

$ echo $DOCKER_HOST
$ firefox $DOCKER_HOST:8080

How to open ports manually with SSH tunneling

Let's say you create a container and want to run something like a Spring Boot app on it.  The container gets a private ip accessible to the virtual machine running it, your desktop or laptop only knows the address of that virtual machine and nothing in it.

Let's solve that problem with an ssh tunnel to it!

Give yourself ssh access to the virutal machine

Copy your public key

copy ~/.ssh/id_rsa.pub to clipboard

Connect to your virtual machine

docker-machine ssh local

Now add your key to authorized keys

vim ~/.ssh/authorized_keys

Now exit back to your terminal

Create a tunnel to the container running on the virtual machine

List the virtual machines running and grab it's ip address

docker-machine ls

NAME      ACTIVE   DRIVER       STATE     URL                         SWARM   DOCKER    ERRORS
default   -        virtualbox   Stopped                                       Unknown   
local     *        virtualbox   Running   tcp://192.168.99.100:2376           v1.10.2   

Now we need the ip of the container running on that virtualmachine, but first lets start the container

$ docker images
REPOSITORY                                 TAG                 IMAGE ID            CREATED             SIZE
springio/gs-spring-boot                    1.0-SNAPSHOT        1eef2782ff99        2 hours ago         195.1 MB
hello-world                                latest              690ed74de00f        5 months ago        960 B

Now start it

$ docker run springio/gs-spring-boot:1.0-SNAPSHOT

Now let's grab the containers id

$ docker ps
CONTAINER ID        IMAGE                                  COMMAND                  CREATED             STATUS              PORTS               NAMES
f39c5f11e51f        springio/gs-spring-boot:1.0-SNAPSHOT   "java -Djava.security"   23 minutes ago      Up 23 minutes                           angry_raman

docker inspect f39c5f11e51f 

            "Networks": {
                "bridge": {
                    ...
                    "Gateway": "172.17.0.1",
                    "IPAddress": "172.17.0.2",
                    ...
                }
            }
 

Now launch the tunnel

ssh -L 1234:<container ip>:8080 docker@<machine ip>

Doing so will allow you to visit localhost:1234, and see what's on the remote 8080 machine.