• Download and install the RaspBerry Pi Imager
• Copy “RaspBerryPi OS Lite” to the SD card

• Boot from SD card
• Update all packages
• Enable SSH server in Interface Options and set location and keyboard in Localisation Options:

  sudo raspi-config

• Change host name
• Config SSH and generate SSH keys
• Exchange public key files
• Install missing packets:

  apt install autossh vim

Install AutoSSH on a remote_host to connect to my main server (local_host) to allow connections from any_host (either at the local location, or at any other remote location) back to the remote host.

1. Verify access from local_host and any_host: SSH from remote_host to local_host:<ssh_port_local_host> with key pair authentication and establish tunnel, requires <ssh_port_local_host> to be open on local location:

   remote_host$ ssh -R <port_to_access_remote_from_local>:localhost:22 user@<domain_name_of_local_host> -p <ssh_port_local_host>

2. Once confirmed, create file autossh-tunnel.service in /etc/systemd/system/:

   [Unit]
   Description=AutoSSH tunnel service Remote port <port_to_access_remote_from_local> to local 22
   After=network.target
   
   [Service]
   Environment="AUTOSSH_GATETIME=0"
   ExecStart=/usr/bin/autossh -o "ServerAliveInterval 10" -o "ServerAliveCountMax 3" -N -R <port_to_access_remote_from_local>:localhost:22 user@<domain_name_of_local_host> -p <ssh_port_local_host> -i /home/pi/.ssh/id_ecdsa
   
   [Install]
   WantedBy=multi-user.target

1. Verify: SSH from local_host to remote_host through tunnel at <port_to_access_remote_from_local>

   local_host$ ssh pi@localhost -p <port_to_access_remote_from_local>

1. Verify: SSH to local_host and establish tunnel from (any_host) <port_to_access_remote_from_local> to localhost:<port_to_access_remote_from_local>
2. Verify: SSH from any_host to localhost:<port_to_access_remote_from_local>

• SSH tunneling with Autossh