I've set this up a few times from scratch so I figured I would automate the process and share. This is a set of shell scripts to make a linux server accessible when it is behind a firewall and/or NAT device without opening inbound network access. It uses the ssh remote port forwarding feature to open a port on a bastion server that forwards back to sshd on the target machine. It also uses autossh to make the connection persistent and upstart to start autossh at boot.

This setup requires ssh network connectivity outbound from the target machine to the bastion server.

This has been tested on Ubuntu 12.04 and 14.04. Use at your own risk!

Open a new terminal session on the bastion machine. Execute the following command.

curl -s https://raw.githubusercontent.com/billmoritz/autossh-reverse-tunnel/master/bastion.sh | sudo bash 

Open a new terminal session on the target machine. Replace the bastion.example.com hostname in the following command and execute it.

curl -s https://raw.githubusercontent.com/billmoritz/autossh-reverse-tunnel/master/target.sh | sudo bash -s bastion.example.com

Go back the bastion terminal and delete the temporate password by running: sudo passwd -d autossh

To ssh to the target from the bastion ssh to localhost on port 10022.

ssh localhost -p 10022