Create a Docker volume - blitterated/docker-dev-env GitHub Wiki

Or, why using Docker volumes is a bad idea for development.

The volumes are stored inside the Linux kernel instance that is the host for all the guest docker kernels, and not via a bind mount to the filesystem of the host OS. Of course if your root OS is Linux, then it will be available on the root filesystem, but it's still technically a folder managed by Docker.

In other words, use a bind mount, not a volume if you want your code accessible to the host OS and the Docker container.

Create a new volume

docker volume create my-vol

Setup git and pull a repo down into the volume

Mount the volume to a container

docker run -it --rm --init -v my-vol:/foo ubuntu bash

Install git

apt update
apt install git

Clone a git repo into the volume

Just for fun, we'll use nsenter1's repository for the example.

cd /foo
git clone https://github.com/justincormack/nsenter1.git
ls nsenter1

Exit the container

exit

View the volume with nsenter1

Fire up the nsenter1 container

docker run -it --rm --privileged --pid=host justincormack/nsenter1

Peek at where the volume is stored on the Docker Linux VM image

NOTE: This is not a container at this point. You've entered the Linux VM where Docker containers are run. This is the intermediary Linux VM that sits between Mac OS and Docker containers.

ls /var/lib/docker/volumes/my-vol/_data/nsenter1/

Exit nsenter1

exit

Bind mount the volume to Mac OS

Yeah, you can't do this. The bind mount would overlay any existing folders on the container. It throws an error anyway.

mkdir bar
docker run -it --rm --init \
           --mount type=volume,source=my-vol,target=/foo \
           --mount type=bind,source="$(pwd)"/bar,target=/foo \
           ubuntu bash

docker: Error response from daemon: Duplicate mount point: /foo.