I installed grandnode from digitalocean marketplace and created user for database access :

db.createUser(
{
user: "saasdbadmin",
pwd:  "saasdbadmin123456",
roles:[{role: "userAdmin" , db:"saasdb"}]
})

and open assess :

vim /etc/mongod.conf

Set
bindIp: 0.0.0.0

And Enabled security :

security:
authorization:enabled

but after some time server hacked and they demand : You must pay 0.04 BTC to 18kq243QoqN97MAqLE1EALbXAWz9PPh31n 48 hours for recover it