dennisfoconnor/dind repository overview

⁠Docker-in-Docker

This recipe lets you run Docker within Docker.

This fork requires Docker v1.8+. For previous versions of Docker see the original DIND⁠

⁠Quickstart

Build the image:

docker build -t dind .

Run Docker-in-Docker and get a shell where you can play, and docker daemon logs to stdout:

docker run --privileged -t -i dind

Run Docker-in-Docker and get a shell where you can play, but docker daemon logs into /var/log/docker.log:

docker run --privileged -t -i -e LOG=file dind

Run Docker-in-Docker and expose the inside Docker to the outside world:

docker run --privileged -d -p 4444 -e PORT=4444 dind

Note: when started with the PORT environment variable, the image will just the Docker daemon and expose it over said port. When started without the PORT environment variable, the image will run the Docker daemon in the background and execute a shell for you to play.

⁠Daemon configuration

You can use the DOCKER_DAEMON_ARGS environment variable to configure the docker daemon with any extra options:

docker run --privileged -d -e DOCKER_DAEMON_ARGS="-D" dind

⁠How It Works

The main trick is to have the --privileged flag. Then, there are a few things to care about:

• /var/lib/docker cannot be on AUFS, so we make it a volume.

That's it.

⁠Important Warning About Disk Usage

Since AUFS cannot use an AUFS mount as a branch, it means that we have to use a volume. Therefore, all inner Docker data (images, containers, etc.) will be in the volume. Remember: volumes are not cleaned up when you docker rm, so if you wonder where did your disk space go after nesting 10 Dockers within each other, look no further :-)

⁠Which Version Of Docker Does It Run?

Outside: it will use your installed version.

Inside: the Dockerfile will retrieve the latest docker binary from https://get.docker.io/⁠; so if you want to include your own docker build, you will have to edit it. If you want to always use your local version, you could change the ADD line to be e.g.:

ADD /usr/bin/docker /usr/local/bin/docker

⁠Can I Run Docker-in-Docker-in-Docker?

Yes. Note, however, that there seems to be a weird FD leakage issue. To work around it, the wrapdocker script carefully closes all the file descriptors inherited from the parent Docker and lxc-start (except stdio). I'm mentioning this in case you were relying on those inherited file descriptors, or if you're trying to repeat the experiment at home.

kojiromike/inception⁠ is a wrapper script that uses dind to nest Docker to arbitrary depth.

Also, when you will be exiting a nested Docker, this will happen:

root@975423921ac5:/# exit
root@6b2ae8bf2f10:/# exit
root@419a67dfdf27:/# exit
root@bc9f450caf22:/# exit
jpetazzo@tarrasque:~/Work/DOTCLOUD/dind$

At that point, you should blast Hans Zimmer's Dream Is Collapsing⁠ on your loudspeakers while twirling a spinning top.