Connecting to monogdb with string I'm trying to connect to MongoDB using a MONGO_URL:. This particular database has a username and password. I've created a user to allow readWrite commands and that's the one I'm using.

If I log into the database and use show dbs this is what appears:

admin         0.000GB
myspecial_db  0.000GB
local         0.000GB


I'm trying to access the myspecial_db. 

MONGO_URL: mongodb://username:password@private-network-ip:27017/myspecial_db

When I try and launch my app I get this error in terminal.

MongoError: failed to connect to server [private-network-ip:27017]

What am I missing here?
As mention your error like 


  MongoError: failed to connect to server [private-network-ip:27017]


This error is what you would see if the mongo shell was not able to talk to the mongod server.

As per MongoDB documentation Connection String URI Format The URI format for defining connections between applications and MongoDB instances in the official MongoDB drivers.

The following is the standard URI connection scheme:

mongodb://[username:password@]host1[:port1][,host2[:port2],...[,hostN[:portN]]][/[database][?options]]


For further your ref here