Docker in Docker with cqfd

[eroussy]

I struggled to use cqfd with Docker in Docker.
Especially, I wanted to be able to launch Docker commands inside cqfd without requiring sudo.

Below is how I did it.
Can you confirm to me that this is a good way to do it ?
If yes, I can add this example to the documentation.

Steps to reproduce

• Create Dockerfile and .cqfdrc as below
• Launch cqfd init with this command : CQFD_EXTRA_BUILD_ARGS="--build-arg DOCKER_GID=$(getent group docker | cut -d: -f3)" cqfd init
• Launch cqfd run
• You should see the docker ps output with the cqfd Docker running

How it works
The Docker socket is passed inside cqfd with volume mapping. However, this socket is owned by the Docker group of the host. To be able to use it inside cqfd you need :

• Your user to be part of the docker group
• The docker group to have the same gid inside the cqfd container and on the host

The files
.cqfd/Docker/Dockerfile :

FROM ubuntu:24.04

# Create the docker group before installing docker
# This is needed to have the same docker gid as the host and be able to use
# the docker socket for docker in docker
ARG DOCKER_GID
RUN groupadd -g ${DOCKER_GID} docker
RUN apt-get update && apt-get install -y docker.io

.cqfdrc

[project]
org='sfl'
name='dind'

[build]
command='docker ps'
docker_run_args="-v /var/run/docker.sock:/var/run/docker.sock"
user_extra_groups="docker"
flavors=''