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Docker in Docker setup with VSCode Dev Containers: How to access running docker containers on the host machine – Debian

I am using VSCode dev containers as a golang development environment using the default golang image. I added the following snippet to the Dockerfile to download the Docker CLI:

# Add Docker
RUN apt-get update 
    && apt-get -y install --no-install-recommends 
    apt-transport-https 
    ca-certificates 
    curl 
    gnupg2 
    software-properties-common 
   && curl -fsSL https://download.docker.com/linux/debian/gpg | sudo apt-key add - 
   && add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/debian $(lsb_release -cs) stable" 
   && apt-get update 
   && apt-get -y install --no-install-recommends docker-ce 
   # Clean up
   && apt-get autoremove -y 
   && apt-get clean -y 
   && rm -rf /var/lib/apt/lists/*

# Symlink docker socket
RUN ln -s "/var/run/docker-host.sock" "/var/run/docker.sock"

And added the following mount to the mounts in the devcontainer.json:

"mounts": ["source=/var/run/docker.sock,target=/var/run/docker-host.sock,type=bind"]

This does allow me to access the Docker Daemon running on my local machine. However if I spin up a postgres container:

docker run -e POSTGRES_USER=user -e POSTGRES_PASSWORD=password -p 5432:5432 -d postgres:9

I can connect to it from my local machine but not from inside the Dev Container. Is there any way to specify the networking option when spinning up a Dev Container (e.g. allow host networking or create a shared network)? Or is there another way I can connect to another running docker container from inside my Dev Container?

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3

Answers


  1. 0

    This answer is only good if you are able to run the other container within your Dev Container.

    You can setup your Dev Container with docker-in-docker. This way you can run docker containers within your Dev Container (and thus the networking will work). The Dockerfile would look like this. There’s a medium article that explains this well.

        FROM docker:19.03.12-dind-rootless@sha256:7606255ca83a7f516fae1b78299b79774f1f798ba9fc792a7231e7b0967ddb05
    USER root

    # Change this with your dependencies, note that this uses alpine apk
    RUN apk add git bash curl make vim go

    USER rootless
    ENV DOCKER_HOST=unix:///var/run/user/1000/docker.sock
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  2. 0

    Assuming I understood you problem correctly, you want to:

    • Use docker CLI in you devcontainer
    • Devcontainer is actually using the host’s docker socket
    • Devcontainer spins up a Postgres container
    • Devcontainer should be able to communicate with the Postgres container directly

    Assuming a default setup, both your devcontainer container and your Postgres container should live in the same network. If they do, the devcontainer can communicate with Postgres using the Postgres container’s IP:port. You can use docker inspect command to find that out.

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  3. 0

    If you prefer to remain in the docker-from-docker approach, different from the alternative solution called docker-in-docker proposed by wanheda, you can connect the dev container to your host ports.

    Assuming that you preserve your host’s docker socket mount:

    "mounts": ["source=/var/run/docker.sock,target=/var/run/docker-host.sock,type=bind"]

    you can add this line to your .devcontainer/devcontainer.json file:

    "runArgs": ["--add-host=host.docker.internal:host-gateway"]

    In this way, you give the dev container a way to reach your host’s address by just using the host name host.docker.internal

    I suggest you to read this article, because docker-from-docker has the advantage of lower overhead but it has also some bind mounting limitations.

    Use Docker or Kubernetes from a container

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