Docker vs Docker compose

• Docker: tool to create, deploy, and run containers
• Docker compose: tool to define and manage multi-container Docker applications using a YAML file (docker-compose.yml)

Important commands

• docker compose up - Start containers (add -d to run in background)
• docker compose down - Stop containers (add -v to remove volumes -> data loss)
• docker compose ps - List containers (add -a to see all containers, including stopped ones)
• docker compose logs -f - View logs (add --tail 100 to see last 100 lines,-f to follow logs in real-time)
• docker compose exec <service> <command> - Run command in a running container (e.g., docker compose exec web bash to open a bash shell in the web service)
• docker compose build - Build or rebuild services
• docker compose pull - Pulls images for services defined in the docker-compose.yml file
• docker compose restart - Restart services
• docker compose stop - Stop services without removing them
• docker compose rm - Remove stopped service containers

Config

theoretically, you can just start multiple containers with Docker commands, but Docker compose makes it easier to manage complex applications with multiple services, networks, and volumes.

Example shell script to start a MongoDB and a Node.js web application:

services:
    database:
        image: mongo:noble
        container_name: mongodb
        volumes:
            - todo-db-data:/data/db
        healthcheck:
            test: ["CMD", "mongo", "--eval", "db.adminCommand('ping')"]
            interval: 10s
            timeout: 5s
            retries: 5
        ports:
            - "27017:27017"
        networks:
            - todo-network
        restart: unless-stopped
    web:
        build: .
        container_name: todo-web
        volumes:
            - ./:/app
        ports:
            - "3000:3000"
        depends_on:
            database:
                condition: service_healthy
        environment:
            - MONGODB_URI=mongodb://database:27017/todo-app
        networks:
            - todo-network
        restart: unless-stopped
volumes:
    todo-db-data:
networks:
    todo-network:
        driver: bridge # default

Volumes

Volume types

• Bind mount: local file or directory mounted into a container (e.g., - ./:/app)
• Named volume: managed by Docker, can be reused across containers (e.g., - todo-db-data:/data/db)
• Anonymous volume: created when a container is created, deleted when the container is removed (e.g., - /app/node_modules)

Mounts

• volumes: for persistent data storage (e.g., databases)
• binds: for sharing code/configuration between host and container (e.g., web application code)
• tmpfs: for temporary data storage in memory (e.g., caching)

Example volume usage

say we want to persist MongoDB data and share application code between host and container:

volumes:
    todo-db-data: # named volume for MongoDB data
services:
    database:
        volumes:
            - todo-db-data:/data/db # mount named volume to /data/db in container
    web:
        volumes:
            - ./:/app # bind mount current directory to /app in container

or via command line:

docker volume create todo-db-data
docker run -d -v todo-db-data:/data/db mongo:noble