how to connect to docker images within the same network? - node.js

Question

I am trying to connect my node JS application to my mongoDB without using the ip address. The strategy which I have read up is that I must have both the containers in the same network.
My node JS application looks as below
var express = require('express');
var app = express();
var mongoose = require('mongoose');
var bodyParser = require('body-parser');
var PORT = 4000;
// REQUIRE MIDDLEWARE
var instantMongoCrud = require('express-mongo-crud'); // require the module
mongoose.connect('localhost:27017/user');
var options = { //specify options
host: `localhost:${PORT}`
}
//USE AS MIDDLEWARE
app.use(bodyParser.json()); // add body parser
app.use(instantMongoCrud(options)); // use as middleware
app.listen(PORT, ()=>{
console.log('started');
})
I have run my database mongodb and attached it into a network called nodenetwork.
I then did a build of my docker application as below:
docker build -t sampleapp:v1 . && docker run --net container:mongodb sampleapp:v1
the app runs correctly from the console output. However, I cannot access it via my browser.
I understand that it is because I must expose the port 4000 when i do a docker run as I had done before.
However, the issue is that when I tried to run like this instead
docker build -t sampleapp:v1 . && docker run -p 4000:4000 --net container:mongodb sampleapp:v1
it throws me: docker: Error response from daemon: conflicting options: port publishing and the container type network mode.
AS such, my question how do I modify this command and is this the best way?

Answer 1

You're telling your application that mongodb will be accesible on localhost but it won't, as localhost will be the application container unless you're running it with --net=host and your mongodb container is exposing the 27017 port or is running on --net=host as well.
You could create a docker network and connect both containers (mongodb and app) to it.
Example:
$ docker network create mynetwork --driver bridge
$ docker run -d --name mongodb --net=mynetwork bitnami/mongodb:latest
$ docker run -d --name app -p 4000:4000 --net=mynetwork sampleapp:v1
This will create a DNS record for mongodb with the same name of the container that will be resolvable from any container within your user-defined network.
Another solution will be to use docker-compose:
version: '3'
services:
mongodb:
image: bitnami.mongodb:latest
app:
build: ./
ports:
- 4000:4000
Place this in a file called docker-compose.yml in the same directory where the Dockerfile for sampleapp is and run docker-compose up
As docker-compose creates a user-defined network as well, you can access mongodb using the container DNS record.
In any of the cases, change your application to connect using the DNS provided by docker:
mongoose.connect('mongodb:27017/user');
Read more about docker-compose and user-defined networks here:
https://docs.docker.com/compose/overview/
https://docs.docker.com/network/bridge/