Can't access MongoDB container from NodeJS App - node.js

Question

I'm running an instance of a web application in my Docker container and am also running a MongoDB container so when I launch the web app I can easily connect to the DB on the app's connection page.
The issue is that I'm not sure how to reach the Mongo container from my web app and am not sure if my host/port connection info is correct.
My Docker Setup
As you can see the container is up and running with both mongo and web app services running without errors
I build the two through docker-compose.yml
version: "3.3"
services:
web:
image: grafana-asw-v3
container_name: grafana-asw-v3
restart: always
build: .
ports:
- "13000:3000"
volumes:
- grafana-storage:/var/lib/grafana
stdin_open: true
tty: true
db:
container_name: mongo
image: mongo
environment:
MONGO_INITDB_ROOT_USERNAME: root
MONGO_INITDB_ROOT_PASSWORD: example
volumes:
- grafana-mongo-db:/var/lib/mongo
ports:
- "27018:27017"
volumes:
grafana-mongo-db: {}
grafana-storage: {}
Issue
With everything up and running I'm attempting to connect through the web app, but I seem to be using the wrong connection info...
I assumed to use "hostMachine:port" (roxane:27018), but it's not connecting. Is there something I overlooked here?

Answer 1

There were two changes I had to make to fix this issue:
Modify the bind_ip in mongod.conf via making this change to my docker-compose file
db:
container_name: mongo
image: mongo
environment:
MONGO_INITDB_ROOT_USERNAME: root
MONGO_INITDB_ROOT_PASSWORD: example
volumes:
- grafana-mongo-db:/var/lib/mongo
ports:
- "27018:27017"
command: mongod --bind_ip 0.0.0.0
I needed to refer to the IP address instead of the hostname in the cli in my we application. (Thanks to this answer for help with this one)

Answer 2

Short answer
db service is in the same network than web service not in host network.
As you named your services via container_name you shoud be able to use the connection string mongodb://mongo:27017
Explanation
By default, docker containers run under a bridge network allowing them to communicate without viewing your host network.
When using ports in a compose file, you define that you want to map an internal port of the container to the host port
"27018:27017" => I want to expose the container port number 27017 to the host port number 27018.
As a result, you could expose your web frontend without exposing your mongo service :
version: "3.3"
services:
web:
image: grafana-asw-v3
container_name: grafana-asw-v3
restart: always
build: .
ports:
- "13000:3000"
volumes:
- grafana-storage:/var/lib/grafana
stdin_open: true
tty: true
db:
container_name: mongo
image: mongo
environment:
MONGO_INITDB_ROOT_USERNAME: root
MONGO_INITDB_ROOT_PASSWORD: example
volumes:
- grafana-mongo-db:/var/lib/mongo
volumes:
grafana-mongo-db: {}
grafana-storage: {}