Now that you have learnt how to connect a non-containerized Node.js application to LocalStack, it's time to explore the necessary changes to run the complete application stack in a containerized environment. To achieve this, you will create a Compose file specifying all required services - frontend, backend, database, and LocalStack.

1. Examine the Docker Compose file. 

   The following Docker Compose file defines four services: `backend`, `frontend`, `mongodb`, and `localstack`. The `backend` and `frontend` services are your Node.js applications, while `mongodb` provides a database and `localstack` simulates AWS services like S3.

   The `backend` service depends on `localstack` and `mongodb` services, ensuring they are running before it starts. It also uses a .env file for environment variables. The frontend service depends on the backend and sets the API URL. The `mongodb` service uses a persistent volume for data storage, and `localstack` is configured to run the S3 service. This setup lets you to develop and test your application locally with AWS-like services.

   ```yaml
   services:
     backend:
       build:
         context: ./backend
         dockerfile: Dockerfile
       ports:
         - 5000:5000
       depends_on:
         - localstack
         - mongodb
       env_file:
         - backend/.env

     frontend:
       build:
         context: ./frontend
         dockerfile: Dockerfile
       ports:
         - 5173:5173
       depends_on:
         - backend
       environment:
         - REACT_APP_API_URL=http://backend:5000/api

     mongodb:
       image: mongo
       container_name: mongodb
       volumes:
         - mongodbdata:/data/db
       ports:
         - 27017:27017

     localstack:
       image: localstack/localstack
       container_name: localstack
       ports:
         - 4566:4566
       environment:
         - SERVICES=s3
         - GATEWAY_LISTEN=0.0.0.0:4566
       volumes:
         - ./localstack:/docker-entrypoint-initaws.d"

   volumes:
     mongodbdata:
   ```