The initial Docker upstart script will not work because it runs on `127.0.0.1`, which is not accessible to the host machine. Instead, we need to change the script to connect to `0.0.0.0`. To do this, modify `/etc/init/docker.conf` to look like this:
Once that's done, you need to set up an SSH tunnel between your host machine and the vagrant machine that's running Docker. This can be done by running the following command in a host terminal:
(The first 2375 is what your host can connect to, the second 2375 is what port Docker is running on in the vagrant machine, and the 2222 is the port Vagrant is providing for SSH. If VirtualBox is the VM you're using, you can see what value "2222" should be by going to: Network > Adapter 1 > Advanced > Port Forwarding in the VirtualBox GUI.)