Here’s the basic Docker Compose file structure.

version: "3.7"

services:
  app:
    container_name: knote-app
    image: learnitguide/knotejs:1.0
    environment:
      - MONGO_URL=mongodb://mongo_db_host:27017/dev
    ports:
      - "80:3000"
    depends_on:
      - mongo
    links:
      - mongo:mongo_db_host

  mongo:
    container_name: knote-mongo
    image: mongo
    ports:
      - "27017:27017"

Explanation:

• version: "3.7": This specifies the version of Docker Compose being used.
• services: Defines the services (containers) in the application.
  • app: Your application container.
    • container_name: The name of the container.
    • image: The Docker image used to build the container.
    • environment: Environment variables, like the MongoDB URL.
    • ports: Maps port 3000 of the container to port 80 on the host machine.
    • depends_on: Specifies that the app service depends on the mongo service.
    • links: Allows the app to link to the mongo container via the alias mongo_db_host.
  • mongo: MongoDB service.
    • container_name: Name of the MongoDB container.
    • image: The MongoDB Docker image.
    • ports: Maps the default MongoDB port 27017 to the host machine.