Yes, I know we could log on server via password or ssh. In the referred article, Arunoda wrote that:
First you need to create SSH tunnel to the server’s MongoDB server.
sudo ssh -L 29017:localhost:27017 root@ip
This command and the port 29017 get me confused.
Following your guide, I wonder this might be unneccssary, at least for now.
And I used ssh private key too, following the best practice~