Add existing VM/Host to docker-machine

I use Docker a lot in my development lifecycle and like to manage my instances with Docker Machine, a powerful tool for provisioning and managing your Dockerized instances with docker-machine commands.

Docker Machine has a driver plugin architecture and the generic driver is useful if you are using a provider that it does not support directly or if you would like to import an existing host. This is how I go about adding my existing host(s).

Add newuser

Use adduser to add new user on remote host.

$ adduser $USER

Add password-less sudo privileges

Use visudo to add new configuration file on remote host.

$ sudo visudo -f /etc/sudoers.d/passwdless-users

and add $USER ALL=(ALL) NOPASSWD:ALL. Save and exit.

Configure Key-based Authentication

On your localhost, generate a SSH key pair.

$ ssh-keygen -b 4096

Copy your public key to remote host using ssh-copy-id.

$ ssh-copy-id $USER@REMOTE_HOST

Create machine

To create a machine, specify --driver generic, the IP address or DNS name of the host and the path to the SSH private key authorized to connect to the host.

$ docker-machine create --driver generic \
 --generic-ip-address REMOTE_HOST_IP \
 --generic-ssh-user $USER \
 --generic-ssh-key ~/.ssh/id_rsa \
 REMOTE_HOST

When the machine is created, Docker generates a unique SSH key and stores it in ~/.docker/machines. This is used under the hood to access the host directly with the docker-machine ssh command.

To connect your Docker client to the Docker Engine running on this instance, run:

eval $(docker-machine env REMOTE_HOST)

E.g, docker-machine inspect REMOTE_HOST lists the machine details.

To disconnect, run:

eval $(docker-machine env -u)

Hope someone finds this helpful.