I get the following error:

Warning { MongoError: failed to connect to server [mongodb:27017] on first connect
    at Pool.<anonymous> (/Users/michaelks/Desktop/users/node_modules/mongodb-core/lib/topologies/server.js:325:35)
    at emitOne (events.js:96:13)
    at Pool.emit (events.js:188:7)
    at Connection.<anonymous> (/Users/michaelks/Desktop/users/node_modules/mongodb-core/lib/connection/pool.js:270:12)
    at Connection.g (events.js:292:16)
    at emitTwo (events.js:106:13)
    at Connection.emit (events.js:191:7)
    at Socket.<anonymous> (/Users/michaelks/Desktop/users/node_modules/mongodb-core/lib/connection/connection.js:173:49)
    at Socket.g (events.js:292:16)
    at emitOne (events.js:96:13)
    at Socket.emit (events.js:188:7)
    at connectErrorNT (net.js:1025:8)
    at _combinedTickCallback (internal/process/next_tick.js:74:11)
    at process._tickCallback (internal/process/next_tick.js:98:9)
  name: 'MongoError',
  message: 'failed to connect to server [mongodb:27017] on first connect' }

Even though I get this in the terminal window where I run Mongo:

2016-12-25T03:45:23.715+0100 I NETWORK [initandlisten] connection accepted from 127.0.0.1:58868 #8 (8 connections now open) 

It kinda looks like there is a connection..

I've tried both

$ mongod 

and

$ brew services start mongo 

This is my test_helper.js

const mongoose = require('mongoose');
mongoose.connect('mongodb:localhost/users_test');
mongoose.connection
 .once('open', () => console.log('Good to go!'))
 .on('error', (error) => {
 console.warn('Warning', error);
 });

I have not specifically made the db "users_test" as I am under the impression that mongoose or mongo or both will do this on the fly.

I've tried both "localhost" and "127.0.0.1?". I'm on OSX 10.11.5 I'm running Node 7.3.0 and Mongo 3.2.9

What am I doing wrong? How do I figure out what's wrong?

Adding one more answer as the solution is from different contexts:

MongoDb Atlas problem solution

I connected to MongoDB Atlas and whitelisted my machine's IP by following the below steps:

• Go to the security tab

• Go to the network access tab under the security tab

• Go to the IP whitelist tab

• Enter the IP address of your machine

I was getting same error while I tried to connect mlab db that is because my organization network has some restriction, I switched to mobile hotspot and it worked.

I ran into this issue serval times, and here is some troubleshooting list

1. make sure database path is exist, the default path in windows in C:\data\db
2. make sure mongo is running, to run it go to C:\Program Files\MongoDB\Server\3.4\bin and run the following:
   1. mongod.exe
   2. mongo.exe
3. make sure that your connection string is correct like mongodb://localhost/database-name

if it is cluster MongoDB then you need to add your current IP to the cluster, to add your current IP address you need to complete few steps below-

step 1- go to login page of Mongodb and login with valid credential - https://cloud.mongodb.com/user#/atlas/login
step 2- CLick Network Access from left sidebar under Security Section
Step 3 - Click Add IP Address
Step 4 - Click Add Current IP Address or Allow Connection From Any Where
now try to connect - npm start

and for Local MongoDB use mongo String like "mongodb+srv://username:pass%[email protected]/test?retryWrites=true&w=majority"

password must be encoded like example string

While connected to a wifi network, mongodb://localhost/db_name worked as expected.

When I wasn't connected to any wifi network, this couldn't work. Instead I used, mongodb://127.0.0.1/db_name and it worked.

Probably a problem to do with ip configurations.

For me,issue was mongo was not running.So first i started "mongod" command in the console.And later in another console tab I have run "mongo". Now the connection is successful. Now run your app your problem should be solved.

I was running mongod in a PowerShell instance. I was not getting any output in the powershell console from mongod. I clicked on the PowerShell instance where mongod was running, hit enter and and execution resumed. I am not sure what caused the execution to halt, but I can connect to this instance of mongo immediately now.

I was trying to connect mlab with my company wifi connection and it was giving this error. But when I switched to personal network it worked and got connected.

In case of remote db in cloud such as ATLAS, you should create whitelist entry 0.0.0.0/0. This allows you to access your cluster ATLAS from any IP address.

Local MongoDb problem solution

solve it by following the below steps:

Changed

mongodb://localhost:27017/local

to

localhost/local

And the error gone

I connected to a VPN and it worked. I was using school's WiFi.

If the mongo instance is build on the cloud.mongodb.com this error appears when the instance can work only from known IP addresses set in the IP whitelist pool when the instance was configured.

So from the mongo dashboard need to be set the current IP address on the IP whitelist from network access menu on the left.

BR,

I tried all the method above.

• Allowed access from any db,
• Verified correct credentials of connection string,
• Created another user,

Nothing of those worked for me.

Finally, I created a new DB and switched to it. everything was fine. Luckily, it wasn't so important DB (for self education purpose) so the damage wasn't so big.