docker-autossh

Highly customizable AutoSSH docker container

Overview

jnovack/autossh is a small lightweight (8.07MB) image that attempts to provide a secure way to establish an SSH Tunnel without including your keys in the image itself or linking to the host.

There's thousands of autossh docker containers, why use this one? I hope you find it easier to use. It's smaller, more customziable, it is an automated build, so there's no sneakiness, and I hope you learn something!

Description

autossh is a program to start a copy of ssh and monitor it, restarting it as necessary should it die or stop passing traffic.

Before we begin, I want to define some terms.

local - THIS docker container.
target - The endpoint and ultimate destination of the tunnel.
remote - The 'middle-man', or proxy server you are tunnelling through to get to your target.
source - The initial endpoint you are starting from that does not have access to the target endpoint, but does have access to the remote endpoint.

The local machine is USUALLY the same as the target but since we are using Docker, we have to abstract out the local endpoint from the target. This is where autossh is usually run from.

Typically, the target can be on a Home LAN segment without a publicly addressible IP address; whereas the remote machine has an address that is reachable by both target and source. And source can only reach remote.

target ---> |firewall| >--- remote ---< |firewall| <--- source 10.1.1.101 [public.ip.addr] 192.168.1.101

Setup

To start, you will need to generate an SSH key. This will ensure the key for the container is separate from your normal user key in the event there is ever a need to revoke one or the other.

$ ssh-keygen -t rsa -b 4096 -C "autossh"
Generating public/private rsa key pair.
Enter file in which to save the key (/home/jnovack/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/jnovack/.ssh/id_rsa.
Your public key has been saved in /home/jnovack/.ssh/id_rsa.pub.
The key fingerprint is:
00:11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff jnovack@yourmom
The key's randomart image is:
+-----[ RSA 4096]-----+
|     _.-'''''-._     |
|   .'  _     _  '.   |
|  /   (_)   (_)   \  |
| |  ,           ,  | |
| |  \`.       .`/  | |
|  \  '.`'""'"`.'  /  |
|   '.  `'---'`  .'   |
|     '-._____.-'     |
+---------------------+

Command-line Options

What would a docker container be without customization? I have an extensive list of environment variables that can be set.

Environment Variables

SSH_HOSTUSER

Specify the usename on the remote endpoint. (Default: root)

SSH_HOSTNAME

Specify the address (ip preferred) of the remote endpoint. (Default: localhost)

SSH_TUNNEL_REMOTE

Specify the port number on the remote endpoint which will serve as the tunnel entrance. (Default: random > 32768) If you do not want a new port every time you restart jnovack/autossh you may wish to explicitly set this.

SSH_TUNNEL_HOST

Specify the address (ip preferred) of the target.

SSH_TUNNEL_LOCAL

Specify the port number on the target endpoint which will serve as the tunnel exit, or destination service. Typically this is ssh (port: 22), however, you can tunnel other services such as redis (port: 6379), elasticsearch (port: 9200) or good old http (port: 80) and https (port: 443).

jnovack / docker-rpi-autossh