nomad-docker-wrapper

This is a hack to allow Docker bind mounts in Nomad. Inspired by how Weave interacts with the Docker daemon by wrapping the Docker socket and augment certain API calls with extra network configuration, this tool allows us to specify Docker bind mounts as environment variables.

Requirements

• The Docker socket must listen on a unix socket

Building

make

Usage

Run sudo ./nomad-docker-wrapper. This will create a new unix socket at /tmp/nomad-docker-wrapper.sock that we can tell Nomad to use by setting docker.endpoint to unix:///tmp/nomad-docker-wrapper.sock.

Now we can create Nomad tasks like this:

task "webservice" {
    driver = "docker"
    config = {
        image = "redis"
    }
    env = {
        DOCKER_BIND_MOUNT = "/some-path:/some-path:ro"
    }
}

When Nomad tell Docker to create this container, nomad-docker-wrapper will modify the API request body by removing the DOCKER_BIND_MOUNT environemnt variable, and add it as an bind mount instead! Kind of ugly, but it seems to work :-) If you want multiple binds you can just suffix the key with something, for example numbers:

env = {
	DOCKER_BIND_MOUNT_1 = "/some-path:/some-path:ro"
	DOCKER_BIND_MOUNT_2 = "/some-other-path:/some-other-path:rw"
	DOCKER_BIND_MOUNT_3 = "/you/get/the/point:/meh:rw"
}

Configuration

You can configure nomad-docker-wrapper with the following environment variables:

• DOCKER_HOST: Location of the Docker unix socket (defaults to unix:///var/run/docker.sock)
• WRAPPER_SOCKET: Location of the wrapper socket (defaults to /tmp/nomad-docker-wrapper.sock)