How do I assign a port mapping to an existing Dock

Question

I'm not sure if I've misunderstood something here, but it seems like it's only possible to set port mappings by creating a new container from an image. Is there a way to assign a port mapping to an existing Docker container?

Answer 1

In Fujimoto Youichi's example test01 is a container, whereas test02 is an image.

Before doing docker run you can remove the original container and then assign the container the same name again:

$ docker stop container01
$ docker commit container01 image01
$ docker rm container01
$ docker run -d -P --name container01 image01

(Using -P to expose ports to random ports rather than manually assigning).

Answer 2

If by "existing" you mean "running", then it's not (currently) possible to add a port mapping.

You can, however, dynamically add a new network interface with e.g. Pipework, if you need to expose a service in a running container without stopping/restarting it.

Answer 3

You can change the port mapping by directly editing the hostconfig.json file at /var/lib/docker/containers/[hash_of_the_container]/hostconfig.json

You can determine the [hash_of_the_container] via the docker inspect <container_name> command and the value of the "Id" field is the hash.

1) stop the container 
2) change the file
3) restart your docker engine (to flush/clear config caches)
4) start the container

So you don't need to create an image with this approach. You can also change the restart flag here.

P.S. You may visit https://docs.docker.com/engine/admin/ to learn how to correctly restart your docker engine as per your host machine. I used sudo systemctl restart docker to restart my docker engine that is running on Ubuntu 16.04

Answer 4

If you run docker run <NAME> it will spawn a new image, which most likely isn't what you want.

If you want to change a current image do the following:

docker ps -a

Take the id of your target container and go to:

cd /var/lib/docker/containers/<conainerID><and then some:)>

Stop the container:

docker stop <NAME>

Change the files

vi config.v2.json

"Config": {
    ....
    "ExposedPorts": {
        "80/tcp": {},
        "8888/tcp": {}
    },
    ....
},
"NetworkSettings": {
....
"Ports": {
     "80/tcp": [
         {
             "HostIp": "",
             "HostPort": "80"
         }
     ],

And change file

vi hostconfig.json

"PortBindings": {
     "80/tcp": [
         {
             "HostIp": "",
             "HostPort": "80"
         }
     ],
     "8888/tcp": [
         {
             "HostIp": "",
             "HostPort": "8888"
         } 
     ]
 }

Restart your docker and it should work.

Answer 5

As a complement of the response of @Fujimoto-Youichi

You can also use $ docker run -P CONTAINER to map ports randomly while creating your container, but be careful with security ascpect !

-P eq to --publish-all : "It publish all exposed ports to random ports" ,

then run docker inspect CONTAINER to fin ports mapping as shown in the image below :

.

Read more about docker run -P in docker run

Answer 6

we an use handy tools like ssh to accomplish this easily.

I was using ubuntu host and ubuntu based docker image.

1. Inside docker have openssh-client installed.
2. Outside docker (host) have openssh-server server installed.

when a new port is needed to be mapped out,

inside the docker run the following command

ssh -R8888:localhost:8888 <username>@172.17.0.1

172.17.0.1 was the ip of the docker interface (you can get this by running ifconfig docker0 | grep "inet addr" | cut -f2 -d":" | cut -f1 -d" " on the host).

here I had local 8888 port mapped back to the hosts 8888. you can change the port as needed.

if you need one more port, you can kill the ssh and add one more line of -R to it with the new port.

I have tested this with netcat.