Shree krishna lamichhane
Shree Krishna Lamichhane

Shree Krishna Lamichhane

Update existing docker container's port mapping without creating new container

Simple and easy way to reconfigure your existing docker container's port mapping.

Shree krishna lamichhane
·Apr 25, 2022·

2 min read

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You forgot to expose a port in container? Don't worry, I have a solution to your problem.

Just follow these steps.

Step 1 : Stop the container you want to modify.

sudo docker stop [containerId]

Step 2: Stop your docker service

To stop the docker.service, first we have to stop docker.socket. Otherwise, it will retrigger to start the docker.service again. So first stop the docker.socket with :

sudo systemctl stop docker.socket

and then docker.service with

sudo systemctl stop docker.service

You can verify whether the service has been stopped or not by using following command.

sudo systemctl status docker

It should output something like this

image.png

Now we are good to proceed.

Step 3 : Update the container's config.v2.json

This file will be located under

/var/lib/docker/containers/[containerId]/config.v2.json

// or if docker is installed as snap
/var/snap/docker/common/var-lib-docker/containers/[containerId]
/config.v2.json

For this example, lets say we want to expose the port 8000.

  • (a) Update entry for “ExposedPorts”

  • (b) Update entry for “Ports”

So update the file as

...
{
"Config": {
....
"ExposedPorts": {
"80/tcp": {},
"8000/tcp": {} //New port number to be exposed
},
....
},
"NetworkSettings": {
....
"Ports": {
 "80/tcp": [
 {
 "HostIp": "",
 "HostPort": "80"
 }
 ], 

//-------- Start ---------
 "8000/tcp": [ //New added port's mapping
 { 
 "HostIp": "",  // IP address of the container
 "HostPort": "8000" //Container's internal port that needs to be exposed. 
 } 
 ] 
//-------- End ---------
 },
....
}

ctrl+x

y

Enter

To save and exit

Step 4 : Update the container's hostconfig.json

This file will be located under

/var/lib/docker/containers/[containerId]/hostconfig.json

// or if docker is installed as snap

/var/snap/docker/common/var-lib-docker/containers/[containerId]
/hostconfig.json
  • (a) Update entry for “PortBindings”
....
 "PortBindings": {
 "80/tcp": [
 {
 "HostIp": "",
 "HostPort": "80"
 }
 ],
 "8000/tcp": [ //new added port 
 {
 "HostIp": "", // IP address of the host container.
 "HostPort": "8000" //Container's internal port that needs to be exposed. 
 }
 ]
 },
.....

ctrl+x

y

Enter

To save and exit

Thats it, your port mapping has been updated.

Now start the container service again with

sudo systemctl start docker

Then start the modified container

sudo docker start [containerId]

Note: The port mapping in docker ps will not be modified unless the container is restarted.

Once the modified container has been started, check status with

docker ps

and you will see the modified port changes.

Hope this helps you. And Happy Coding !

 
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