I have a container based application running node JS and my backend is a mongoDB container.

Basically, what I am planning to do is to run this in kubernetes.

I have deployed this as separate containers on my current environment and it works fine. I have a mongoDB container and a node JS container.

To connect the two I would do

docker run -d --link=mongodb:mongodb -e MONGODB_URL='mongodb://mongodb:27017/user' -p 4000:4000 e922a127d049 

my connection.js runs as below where it would take the MONGODB_URL and pass into the process.env in my node JS container. My connection.js would then extract the MONGODB_URL into the mongoDbUrl as show below.

const mongoClient = require('mongodb').MongoClient;
const mongoDbUrl = process.env.MONGODB_URL;
//console.log(process.env.MONGODB_URL)
let mongodb;

function connect(callback){
    mongoClient.connect(mongoDbUrl, (err, db) => {
        mongodb = db;
        callback();
    });
}
function get(){
    return mongodb;
}

function close(){
    mongodb.close();
}

module.exports = {
    connect,
    get,
    close
};

To deploy on k8s, I have written a yaml file for

1) web controller 2) web service 3) mongoDB controller 4) mongoDB service

This is my current mongoDB controller

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: mongo-deployment
spec:
  replicas: 1
  template:
    metadata:
      labels:
        name: mongo
    spec:
      containers:
      - image: mongo:latest
        name: mongo
        ports:
        - name: mongo
          containerPort: 27017
          hostPort: 27017

my mongoDB service

apiVersion: v1
kind: Service
metadata:
  labels:
    name: mongodb
  name: mongodb
spec:
  ports:
    - port: 27017
      targetPort: 27017
  selector:
    name: mongo

my web controller

apiVersion: v1
kind: ReplicationController
metadata:
  labels:
    name: web
  name: web-controller
spec:
  replicas: 1
  selector:
    name: web
  template:
    metadata:
      labels:
        name: web
    spec:
      containers:
      - image: leexha/node_demo:21
        env:
        - name: MONGODB_URL
          value: "mongodb://mongodb:27017/user"
        name: web
        ports:
        - containerPort: 4000
          name: node-server

and my web service

apiVersion: v1
kind: Service
metadata:
  name: web
  labels:
    name: web
spec:
  type: NodePort
  ports:
    - port: 4000
      targetPort: 4000
      protocol: TCP
  selector:
    name: web

I was able to deploy all the services and pods on my local kubernetes cluster.

However, when I tried to access the web application over a nodeport, it tells me that there is a connection error to my mongoDB.

TypeError: Cannot read property 'collection' of null
    at /app/app.js:24:17
    at Layer.handle [as handle_request] 

This is my node JS code for app.js

var bodyParser = require('body-parser')
, MongoClient = require('mongodb').MongoClient
, PORT = 4000
, instantMongoCrud = require('express-mongo-crud') // require the module
, express = require('express')
, app = express()
, path = require('path')
, options = { //specify options
    host: `localhost:${PORT}`
}
, db = require('./connection')


// connection to database
db.connect(() => {

    app.use(bodyParser.json()); // add body parser
    app.use(bodyParser.urlencoded({ extended: true }));
    //console.log('Hello ' + process.env.MONGODB_URL)

    // get function 
    app.get('/', function(req, res) {
        db.get().collection('users').find({}).toArray(function(err, data){
            if (err)
                console.log(err)
            else
                res.render('../views/pages/index.ejs',{data:data});
        });
    });

Clearly, this is an error when my node JS application is unable to read the mongoDB service.

I at first thought my MONGODB_URL was not set in my container. However, when I checked the nodeJS container using

kubectl exec -it web-controller-r269f /bin/bash

and echo my MONGODB_URL it returned me back mongodb://mongodb:27017/user which is correct.

Im quite unsure what I am doing wrong as I am pretty sure I have done everything in order and my web deployment is communicating to mongoDB service. Any help? Sorry am still learning kubernetes and please pardon any mistakes