As a DevOps engineer, you need to deploy a web application with a Node.js backend and a MySQL database using Docker. The Node.js app connects to MySQL on localhost:3306, but running docker run for each container separately fails because they can’t communicate. How would you set up these containers to work together?

To make the Node.js and MySQL containers communicate:

1. Use Docker Compose: Create a docker-compose.yml file to define and link both services:

   version: '3.8'
   services:
     node-app:
       image: my-node-app
       build: .
       ports:
         - "3000:3000"
       depends_on:
         - mysql-db
       environment:
         - DB_HOST=mysql-db
         - DB_PORT=3306
     mysql-db:
       image: mysql:8.0
       environment:
         - MYSQL_ROOT_PASSWORD=secret
       ports:
         - "3306:3306"
   

2. Run the Application: Execute docker-compose up -d to start both containers. The node-app service connects to mysql-db using the service name (mysql-db) as the hostname, not localhost.
3. Verify Connectivity: Check logs with docker-compose logs node-app to ensure the Node.js app connects to MySQL. If it fails, verify the environment variables and MySQL’s readiness.
4. Alternative Without Compose: Use a custom network:
   • Create a network: docker network create my-app-network
   • Run MySQL: docker run -d --name mysql-db --network my-app-network -e MYSQL_ROOT_PASSWORD=secret mysql:8.0
   • Run Node.js: docker run -d --name node-app --network my-app-network -p 3000:3000 -e DB_HOST=mysql-db my-node-app