Docker in Docker cannot mount volume

Question

I am running a Jenkins cluster where in the Master and Slave, both are running as a Docker containers.

The Host is latest boot2docker VM running on MacOS.

T

Answer 1

A way to work around this issue is to mount a directory (inside your docker container in which you mounted your docker socket) using the exact same path for its destination. Then, when you run a container from within that container, you are able to mount anything within that mount's path into the new container using docker -v.

Take this example:

# Spin up your container from which you will use docker
docker run -v /some/dir:/some/dir -v /var/run/docker.sock:/var/run.docker.sock docker:latest

# Now spin up a container from within this container
docker run -v /some/dir:/usr/src/app $CONTAINER_IMAGE

The folder /some/dir is now mounted across your host, the intermediate container as well as your destination container. Since the mount's path exists on both the host as the "nearly docker-in-docker" container, you can use docker -v as expected.

It's kind of similar to the suggestion of creating a symlink on the host but I found this (at least in my case), a cleaner solution. Just don't forget to cleanup the dir on the host afterwards! ;)