Make multiple Node js dockerized app communcate to mongodb docker

Question

I've built two NEST app which shares a common database. I've been trying to figure out a way to make these two apps to get data from the Mongo db container. I'm stuck with this process.

docker-compose.yml with app 1

version: '3'

services:  
  backend:
    image: 'example-image_1:1.0.0'
    working_dir: /app/example-app-1/backend/example-app-1-api
    environment:
      - DB_URL=mongodb://0.0.0.0:27017/example_app_1
      - BACKEND_PORT=3333
      - BACKEND_IP=0.0.0.0
    restart: always
    network_mode: "host"
    ports:
      - '3333:3333'
    command: ['node', 'main.js']
    depends_on:
      - mongodb

    expose:
      - 3333

  mongodb:
    image: 'mongo:latest'
    environment:
      - 'MONGODB_DATABASE="example_app_1"'
    ports:
      - '27017:27017'
    expose:
      - 27017

docker-compose.yml with app-2

version: '3'

services:   
  backend:
    image: 'example_app_2:1.0.0'
    working_dir: /app/example_app_2/backend/example-app-2-api
    environment:
      - DB_URL=mongodb://0.0.0.0:27017/example_app_2
      - BACKEND_PORT=8888
      - BACKEND_IP=0.0.0.0
    restart: always
    ports:
      - '8888:8888'
    command: ['node', 'main.js']
    expose:
      - 8888

  mongodb:
    image: 'mongo:latest'
    environment:
      - 'MONGODB_DATABASE="example_app_2"'
    ports:
      - '27017:27017'
    expose:
      - 27017

I need help in making these app communicate with common container - mongodb

Click link for Architecture Setup

Answer 1

Since you're using 2 different docker-compose.yml you're actually running 2 backend and 2 mongodb on 2 docker-networks

One of the 2 mongo won't start cause the port is already occupied.

Option 1 (nicer):

services:   
  backend_1:
      ...
    ports:
      - '8888:8888'
  backend_2:
      ...
    ports:
      - '8899:8899'

  mongodb:
    ports:
      - '27017:27017'

This setup provides 3 container on the same network. Now you can access at mongo from both backends at <mongo_ip>:27017

Option 2 (ugly):

services:   
  backend:
      ...
    ports:
      - '8888:8888'

  mongodb:
    ports:
      - '27017:27017'

And in another docker-compose

services:   
  backend:
      ...
    ports:
      - '8888:8888'

This setup provides 3 container on 2 different network. In this setup each docker-compose.yml has it's own docker network, so from the second backend service you have to connect to another docker network to access the container.