Added post on forwarding the Docker socket with SSH.

Docker socket over SSH

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:date: 2018-01-09

:summary: Docker socket over SSH

Yesterday I described how to connect to a remote :code:`dockerd` over TCP. I

didn't touch security considerations at all (firewall, TLS certificate). This

because, for my use, I prefer a different method, forwarding the Unix socket

over SSH. Here's how.

First, you need OpenSSH version 6.7 or later (both client and server). Also,

the login user on the remote instance must have permissions to access the Docker

socket (in other words, be a member of the :code:`docker` group).

Here's how to forward the remote socket:

.. code:: shell

    ssh -fNTo ExitOnForwardFailure=yes -o ServerAliveInterval=30 -L $HOME/.ssh/docker.sock:/var/run/docker.sock host

    export DOCKER_HOST=$HOME/.ssh/docker.sock

And to close the connection and return to the local :code:`dockerd` kill the

:code:`ssh` process that's running in the background, :code:`rm` the docker

socket under :code:`$HOME/.ssh` and unset :code:`DOCKER_HOST`.

The reason I prefer this method is that it's easier to setup for ad-hoc tasks

and arguably more secure since you not only authenticate the user and host with

SSH, but you limit access to only those that are part of the :code:`docker`

group.