Docker compose MongoDB with NodeJS using yarn - node.js

Question

I'm trying to use docker compose to put in containers a node.js server and a mongodb database. I'm also trying to use yarn as my package-manager. My project is codded in typescript and my Mongodb is used as a service for my server.
For what I have at the moment, it works just fine, but I'm not sure if my implementation is even good. When I run docker-compose up, the containers and the images of node.js and mongodb are created, and the containers are running on the specified ports.
The problem is that when I kill the mongodb container, my nodejs server still has access to the database, like if my container mongodb container is still running. I would guess that it's because my mongodb server is also running on the same container as my node.js server.
This is my Dockerfile:
FROM node:lts-alpine
ADD package.json /app/package.json
ADD yarn.lock /app/yarn.lock
WORKDIR /app
# Installing packages
RUN yarn
ADD . /app
ENV NODE_ENV=production
# Building TypeScript files
RUN yarn build
CMD ["node", "./dist/app.js"]
These are the scripts in my package.json file:
"scripts": {
"lint": "eslint src/**/*.ts",
"format": "eslint src/**/*.ts --fix",
"start": "tsc && node --unhandled-rejections=strict ./dist/app.js",
"debug": "export DEBUG=* && npm run start",
"test": "echo \"Error: no test specified\" && exit 1",
"dev": "ts-node src/app.ts",
"build": "rm -rf build && tsc -p ."
},
And this is my docker-compose.yml file:
version: "3"
services:
app:
container_name: app
restart: always
build:
context: .
dockerfile: Dockerfile
env_file: .env
volumes:
- ./src:/app/src
environment:
- COSMOSDB_HOST=${COSMOSDB_HOST}
- COSMOSDB_PORT=${COSMOSDB_PORT}
- COSMOSDB_DBNAME=${COSMOSDB_DBNAME}
- COSMOSDB_USER=${COSMOSDB_USER}
- COSMOSDB_PASSWORD=${COSMOSDB_PASSWORD}
ports:
- "4000:4000"
links:
- mongo
mongo:
container_name: mongo
image: mongo
ports:
- "27017:27017"
volumes:
- ./data:/data/db
I don't seem to understand what's wrong with my files...
Can you help me ? Also, would you have some recommendation to give me to optimize the build or anything else ? Thank you !