Docker, Spring Boot, MongoDB, and yaml files

Think of your computer (the Host) and the Docker container (the Container) as two separate machines.

1. Your Spring Boot App: You run this from your IDE (like IntelliJ or VS Code). It runs directly on your Host machine.
2. Your MongoDB Database: This runs inside the isolated Docker Container.
   • creates a virtual server (a container) that has MongoDB installed inside it
   • Docker reads image: mongo: latest and downloads an official, pre-packaged version of MongoDB → creates an isolated container and installs and runs that MongoDB server in the container!
   • Sees

In docker-compose.yml

# docker-compose.yml
 
version: '3.8'
 
services:
  mongodb:
    image: mongo:latest # Use the official Mongo image
    container_name: monew-mongo-db
    ports:
      - "27017:27017" # Map port 27017 on your machine to port 27017 in the container
    volumes:
      - mongo-data:/data/db # Persist data even if the container is removed
 
volumes:
  mongo-data:

• “Map port 27017 on my Host machine to port 27017 inside the Container.”

Step by Step

• You run docker-compose up. Docker starts the MongoDB container.
• Docker sees ports: - "27017:27017" and creates a network forward. It starts listening on your computer’s localhost:27017.
• You run your Spring Boot application from your IDE (on the Host).
• Spring reads your application-dev.yml and sees uri: mongodb://localhost:27017/monew.
• Your application tries to connect to localhost on port 27017.
• Docker, which is listening on that port, catches this request and forwards it directly to port 27017 inside the MongoDB container, where the database is actually running.

Basically

• You run your Spring Boot application directly from your IDE (IntelliJ, VS Code, Eclipse).
• You run your database using docker-compose up.