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Last pushed: a year ago
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Yet another Docker base image to make it easier to connect to your
running Docker instances.

With a Little Help from Phusion

Based on Phusion's excellent baseimage-docker,
this Docker base-image features all of the awesome features you've grown to love like
working CRON jobs, a SSH server, a lightweight working init system (that actually works!),
and more.

...But Even Better

Phusion's baseimage project is currently debating how best to allow users to connect
to running Docker instances. They provide the OpenSSH daemon but no real way to easily
add your own keys and connect once a Docker image has already been built.

In the interest of modularity, our Docker base-image provides two different ways to add
SSH keys to Docker instances without any build-time tweaks and without requiring external
tools like nsenter

Add SSH Keys with Environment Variables

The first option we provide is to specify SSH keys in an environment variable when starting
your Docker instance:

sudo docker run -d -e SSH_KEYS="$(cat ~/.authorized_keys)" rfkrocktk/baseimage

On startup of the container, it will add each SSH key found in the SSH_KEYS
environment variable to the $HOME/.ssh/authorized_keys file inside of the container. You'll
then be able to quickly and easily SSH into the Docker instance using your key.

Supported Environment Variables

Name Required Description
SSH_KEYS No A newline-delimited list of SSH keys in the authorized_keys file format.
SSH_USER No (Defaults to root) The user to set the SSH keys for, generally root.

Add SSH Keys with a Docker Volume

This is an even easier way to maintain a Docker instance's authorized_keys file. In our base-image,
we've created a directory for each user called $HOME/.ssh/authorized_keys.d/ which contains the authorized_keys file which is then symlinked back to $HOME/.ssh/authorized_keys. What this means
is that you can easily maintain the authorized_keys file outside of the Docker instance by using
a Docker volume:

sudo docker run -d --name "dockerduck" -v /host/path/to/dockerduck-ssh-keys:/root/.ssh/authorized_keys.d \

Now, simply open /host/path/to/dockerduck-ssh-keys/authorized_keys and add your SSH public keys there:

sudo cat ~/.ssh/authorized_keys > /host/path/to/dockerduck-ssh-keys/authorized_keys

Done! Now just connect to your Docker instance!

Note: environment variables will always overwrite $HOME/.ssh/authorized_keys, so don't mix and match. Use one or the other, not both.

Connecting to Your Docker Instance

Now that you've added your keys to your Docker instance, you need to know its internal IP address to
connect to it. You can use the following command to see your Docker instance IP addresses:

sudo docker inspect -f "{{.NetworkSettings.IPAddress}}" dockerduck

In my case, the IP address is, therefore:

ssh root@

Note, you probably have to enable agent-forwarding if you're connecting to a Docker instance
hosted on a remote server, as your agent only runs on your local machine and is terminated on
your first hop.

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