node.js - Error: failed to connect to server [localhost:27017] on first connect [MongoNetworkError: connect ECONNREFUSED 127.0.0.1:27017]

Question

I'm new in nodeJS and mongodb. I learned all these stuffs from YouTube. I tried to create an api using node.js but now I can't even connect to the mongodb.

The problem is I uses Fn project(runtime node) and tried to connect to the mongodb but it didn't work.(The Fn project is an open-source container-native serverless platform.)

This is the part that I use to connect to mongodb:

var MongoClient = require('mongodb').MongoClient;
var url = 'mongodb://localhost:27017/MyDB';

MongoClient.connect(url,function(err, db) {
   if(err) throw err;
   console.log("Database is Connected!");
   db.close();
});

//This is the part that Fn Project generated automatically
var fdk = require('@fnproject/fdk');

fdk.handle(function(input){
var name = 'World';
    if (input.name) {
        name = input.name;
    }
response = {'message': 'Hello ' + name}
return response;
})

So I run the command to start the Fn Server

fn start

and I also run the command to start mongodb

sudo mongod

After everything is set, I run the command to execute the code before deploying.

sudo fn run

and this is the resule that I got:

Building image nodefn:0.0.3 ...
(node:1) DeprecationWarning: current URL string parser is deprecated, and will be removed in a future version. To use the new parser, pass option { useNewUrlParser: true } to MongoClient.connect.
/function/node_modules/mongodb/lib/operations/mongo_client_ops.js:466
      throw err;
      ^

Error: failed to connect to server [localhost:27017] on first connect [MongoNetworkError: connect ECONNREFUSED 127.0.0.1:27017]
    at Pool.<anonymous> (/function/node_modules/mongodb-core/lib/topologies/server.js:564:11)
    at emitOne (events.js:115:13)
    at Pool.emit (events.js:210:7)
    at Connection.<anonymous> (/function/node_modules/mongodb-core/lib/connection/pool.js:317:12)
    at Object.onceWrapper (events.js:318:30)
    at emitTwo (events.js:125:13)
    at Connection.emit (events.js:213:7)
    at Socket.<anonymous> (/function/node_modules/mongodb-core/lib/connection/connection.js:246:50)
    at Object.onceWrapper (events.js:316:30)
    at emitOne (events.js:115:13)

My docker version is Docker version 18.06.1-ce and Ubuntu version is Ubuntu 18.04.1 LTS.

In addition, this is the package.json and func.yaml

{
    "name": "hellofn",
    "version": "1.0.0",
    "description": "backend",
    "main": "func.js",
    "author": "",
    "license": "Apache-2.0",
    "dependencies": {
        "@fnproject/fdk": "0.x",
        "mongodb": "^3.1.4"
    }
}

--

//func.yaml
schema_version: 20180708
name: nodefn
version: 0.0.3
runtime: node
entrypoint: node func.js
format: json
triggers:
    - name: nodefn-trigger
      type: http
      source: /nodefn-trigger

I'm stuck at this error for a week and I am so lost right now.