Configure SSH connection between servers

Manual configuration:

On the GUI server:

# Make an SSH key set special for Passenger Apache
mkdir -p /var/www/.ssh/

# Generate an RSA key with NO passcode
ssh-keygen -f /var/www/.ssh/id_rsa -q -t rsa -N ""

# Make Apache the owner of the keys
chown -R apache:apache /var/www/.ssh/

# Share the public key with the servers
cat /var/www/.ssh/id_rsa.pub | ssh USER@SERVER_IP 'mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys'
# Repeat this step for all the remote servers you want your GUI to connect to (change USER and SERVER_IP correspondingly)