How do I assign a port mapping to an existing Docker container

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

User · Answer

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

I was using ubuntu host and ubuntu based docker image.

Inside docker have openssh-client installed.
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.

User · Answer

I m also interested in this problem   As  Thasmo mentioned  port forwardings can be specified ONLY with docker run  and docker create  command  Other commands  docker start does not have -p option and docker port only displays current forwardings   To add port forwardings  I always follow these steps    stop running container  docker stop test01  commit the container  docker commit test01 test02   NOTE  The above  test02 is a new image that I m constructing from the test01 container  re-run from the commited image  docker run -p 8080 8080 -td test02    Where the first 8080 is the local port and the second 8080 is the container port

User · Answer

If you run docker run  lt NAME gt  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  lt conainerID gt  lt and then some   gt    Stop the container   docker stop  lt NAME gt    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

User · Answer

To change HostPort of a container on Windows 10   list all containers   docker ps -a   docker stop docker101tutorial    Use grep or rg to get Id of container   docker inspect docker101tutorial   grep -i id          quot Id quot    quot sha256 fff0a4b22d6f3d2eb8d2748b8a8bbc9967ea87199988acee8e86ac70bce9c3eb quot     run plain ubuntu docker image with shell and change it s namespace to docker host   https   stackoverflow com questions 60408574 how-to-access-var-lib-docker-in-windows-10-docker-desktop 60411313 60411313   https   forums docker com t the-location-of-images-in-docker-for-windows 19647 4   docker run -it --privileged --pid host ubuntu nsenter -t 1 -m -u -i sh   We want to find out the directory of docker101tutorial container  We are looking for      quot Image quot   quot sha256 fff0a4b22d6f3d2eb8d2748b8a8bbc9967ea87199988acee8e86ac70bce9c3eb quot     in  var lib docker containers   config v2 json   grep -rl --include config v2 json fff0a4b22d  var lib docker containers   var lib docker containers c1eda20b30f058bce9f8ece3b47a21641df5b399770e12ab57416a954d3c8bbf config v2 json   edit it   vi  var lib docker containers c1eda20b30f058bce9f8ece3b47a21641df5b399770e12ab57416a954d3c8bbf hostconfig json   Press i for insert mode  Change  quot HostPort quot   quot 80 quot  to  quot HostPort quot   quot 8092 quot  Press Escape and write  wq  Press Enter  Do not start stop docker101tutorial now  Otherwise changes to HostPort will be reverted  Right click Docker Desktop tray icon and click Restart  In Docker Desktop s list of containers  look at your container  Displayed port should change to 8092  Start your container  Now it will be mapped to port 8092 on host   Based on  holdfenytolvaj answer

User · Answer

Editing hostconfig json seems to not working now  It only ends with that port being exposed but not published to host  Commiting and recreating containers is not the best approach to me  No one mentioned docker network   The best solution would be using reversed proxy within the same network   Create a new network if your previous container not in any named ones   docker network create my network Join your existing container to the created network  docker network connect my network my existing container Start a reversed proxy service e g  nginx  publishing the ports you need  joining the same network  docker run -d --name nginx --network my network -p 9000 9000 nginx  Optionally remove the default conf in nginx  docker exec nginx rm  etc nginx conf d default conf Create a new nginx config  server       listen 9000       location             proxy pass http   my existing container 9000          proxy http version 1 1          proxy set header Upgrade  http upgrade          proxy set header Connection  upgrade           proxy set header Host  host          proxy cache bypass  http upgrade            Copy the config to nginx container   docker cp   my conf conf nginx  etc nginx conf d my conf conf Restart nginx  docker restart nginx   Advantages  To publish new ports  you can safely stop update recreate nginx container as you wish without touching the business container  If you need zero down time for nginx  it is possible to add more reversed proxy services joining the same network  Besides  a container can join more than one network   Edit   To reverse proxy non-http services   the config file is a bit different  Here is a simple example   upstream my service       server my existing container 9000     server       listen 9000      proxy pass my service

User · Answer

Stop the docker engine and that container  Go to  var lib docker containers   container id  directory and edit hostconfig json Edit PortBindings HostPort that you want the change  Start docker engine and container

User · Answer

Not sure if you can apply port mapping a running container  You can apply port forwarding while running a container which is different than creating a new container      docker run -p  lt public port gt   lt private port gt  -d  lt image gt      will start running container  This tutorial explains port redirection

User · Answer

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

User · Answer

For Windows  amp  Mac Users  there is another pretty easy and friendly way to change the mapping port         download kitematic    go to the settings page of the container  on the ports tab  you can directly modify the published port there     start the container again

User · Answer

If you simply want to change the port of the running container  you do    stop existing container     sudo docker stop NAME  now restart with the new port mapping     sudo docker run -d -p 81 80 NAME    where as       -d  to background   deamon the docker       -p  enable port mapping       81  external  exposed  port you use to access with your browser       80  internal docker container listen port

User · Answer

You can change the port mapping by directly editing the hostconfig json file at  var lib docker containers  hash of the container  hostconfig json or  var snap docker common var-lib-docker containers  hash of the container  hostconfig json  I believe  if You installed Docker as a snap  You can determine the  hash of the container  via the docker inspect  lt container name gt  command and the value of the  quot Id quot  field is the hash   Stop the container  docker stop  lt container name gt    Stop docker service  per Tacsiazuma s comment  Change the file  Restart your docker engine  to flush clear config caches   Start the container  docker start  lt container name gt     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

User · Answer

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

User · Answer

If you are not comfortable with Docker depth configuration  iptables would be your friend  iptables -t nat -A DOCKER -p tcp --dport   YOURPORT  -j DNAT --to-destination   CONTAINERIP    YOURPORT   iptables -t nat -A POSTROUTING -j MASQUERADE -p tcp --source   CONTAINERIP  --destination   CONTAINERIP  --dport   YOURPORT   iptables -A DOCKER -j ACCEPT -p tcp --destination   CONTAINERIP  --dport   YOURPORT   This is just a trick  not a recommended way  This works with my scenario because I could not stop the container

[docker] How do I assign a port mapping to an existing Docker container?

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