By default, the MongoDB One-Click application is secured with a UFW-managed firewall. In order to allow your Node application to access the MongoDB instance, you must open a port in the firewall. This command will allow access from the Node app’s IP address and nowhere else:

sudo ufw allow from node_ip_address to any port 27017

Additionally, MongoDB is configured to only listen on the local interface by default. To allow remote connections, modify the value of bindIp in /etc/mongod.conf If you do so, you are highly advised to first review the security checklist from the MongoDB documentation. In addition to enabling one of the forms of authentication supported by MongoDB.

The relevant section of the config file should look like:

# [ ... ]
net:
  port: 27017
  bindIp: 127.0.0.1,ip_of_mongo_droplet
# [ ... ]

For more information on running MongoDB, including enabling authentication, check out:

• How to Install and Secure MongoDB on Ubuntu 16.04