Maintaining a secure connection to a remote host using SSH to securely tunnel traffic for underlying services like MSQL, PostgreSQL or just for remote support is made far easier by using a tool designed to bring up the connection and monitor and maintain it.
This is where autossh comes in.
There are times when a full blown VPN is too much. In this instance al lwe wanted was a remote system to connect to us automatically when it is powered on. We could then remotely connect to it and copy files to and from it.
Our requirement was for a reverse connection, such that the remote host didn’t have any capability to do anything other than connect. We would do all the talking.
Setup an autossh.service
tossh.sevice file and enable it:
$ sudo vi /etc/systemd/system/autossh.service $ sudo systemctl daemon-reload $ sudo systemctl enable autossh.service $ sudo systemctl start autossh.service
[Unit] Description=Keeps a tunnel to '18.104.22.168' open Wants=network-online.target After=network.target network-online.target [Service] User=autossh Restart=always RestartSec=3 # -p [PORT] # -l [user] # -M 0 --> no monitoring # -N Just open the connection and do nothing (not interactive) # LOCALPORT:IP_ON_EXAMPLE_COM:PORT_ON_EXAMPLE_COM Environment="AUTOSSH_GATETIME=0" ExecStart=/usr/bin/autossh -M 0 -N -q -o "StrictHostKeyChecking no" -o "ServerAliveInterval 60" -o "ServerAliveCountMax 3" -p 22 -l userid 22.214.171.124 -R 2201:127.0.0.1:22 -i /home/autossh/.ssh/id_rsa [Install] WantedBy=multi-user.target
126.96.36.199 is our local server running
2201 is the port we will forward to.
On the remote system we created a user called
autossh and generated an ssh key pair for them and installed the public key into our local servers
authorized_keys for our user
Also in the
autohorized_keys we disabled the remote clients ability to do anything with our server other than connect by placing the following before the key eg.
no-X11-forwarding,no-agent-forwarding,no-pty ssh-rsa AAAAB3Nz...
This means the remote system always connects and is always listed as a process on our gateway. This is a good thing as we can use monitoring tools such as Nagios to determine if the remote site is alive.