@viettran

Connecting over an SSH Tunnel is probably the most secure means of connecting, though you also have the option of opening remote connections to the MongoDB instance.

In /etc/mongod.conf there’s a directive named bind_ip which you can set to the IP of the Droplet (and then restart MongoDB). I would, however, recommend ensuring that you’ve setup a firewall and are only allowing access to a limited number of IP’s if you go that route.