kmbulebu/ssh-bastion repository overview

⁠Purpose

This container image provides an SSH server such that remote clients can connect through this server to other SSH servers. This is often necessary in high security environments where firewalls, routing, and addressing prevent direct access to the desired servers.

⁠Sample Usage

This image is not intended to be used directly. You should build upon it to generate unique SSH host keys and add your SSH public keys to the bastion user's authorized_keys file. See sample_usage directory for an example of how to run this container.

cd sample_usage
cat ~/.ssh/id_rsa.pub >> authorized_keys
docker-compose up

Then connect to a server through the bastion:

ssh -A -o ProxyCommand='ssh -W %h:%p -p 2200 bastion@localhost' user@backendserver

In practice localhost would be the hostname of a machine running this container and user@backendserver would be the user and hostname of the machine you wanted to connect.

⁠Updating SSH user config

To avoid using the long form ssh command above, you can add this option to be applied by default in your ssh client user config. It's even possible to use wildcards for host to use the bastion as a proxy for an entire domain.

~/.ssh/config snippet:

Host foo
HostName foo
User me
ProxyCommand ssh -W %h:%p -p 2200 bastion@docker

⁠Notes

• Only support proxying to other SSH hosts.
• Only support SSH public key authentication.
• Lock down ssh daemon.
  • No shell
  • No TTY
  • No password authentication
  • Limit users
  • Stricter rules
• Single user: bastion
• Leverage Docker security features.