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dockerportlxclinux-containers

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

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?

Solution

  • 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 if you installed Docker as a snap.

    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 (docker stop <container_name>).
    2. Stop docker service (per Tacsiazuma's comment)
    3. Change the file.
    4. Restart your docker engine (to flush/clear config caches).
    5. Start the container (docker start <container_name>).

    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.

    Adding ports: As mentioned in the comments you might also want to export the port from the (containered) machine. (For example when a new port appears in docker inspect but not in docker container ls)

    In this case you also have to edit the config.v2.json file (next to hostconfig-file).
    The syntax is like "ExposedPorts":{"8080/tcp":{}} (if you wish to expose port 8080 from the container)