Docker compose basics: Essential commands

Installation and Setup

Understanding the Docker Compose YAML File

// language: yaml
version: '3.8'

services:
  web:
    build: .
    ports:
      - "8000:8000"
    volumes:
      - .:/app
    depends_on:
      - db
    environment:
      - DB_HOST=db
      - DB_USER=user
      - DB_PASSWORD=secret
      - DB_NAME=myapp_db

  db:
    image: postgres:13
    volumes:
      - postgres_data:/var/lib/postgresql/data
    environment:
      - POSTGRES_USER=user
      - POSTGRES_PASSWORD=secret
      - POSTGRES_DB=myapp_db

volumes:
  postgres_data:

• version: '3.8': Specifies the version of the Compose file format.
  • The version field is now officially considered obsolete and is deprecated. The modern docker compose CLI (Compose V2) uses the Compose Specification by default. It's safe to remove this line from your Compose files.
• services: The top-level key defining all the containers in your application.
  • web: A service named web.
    • build: .: Tells Docker Compose to build an image from a Dockerfile in the current directory (.).
    • ports: - "8000:8000": Maps port 8000 on the host to port 8000 in the container.
    • volumes: - .:/app: Creates a bind mount, linking the current host directory to the /app directory inside the container.
    • depends_on: - db: Ensures the db service starts before the web service.
    • environment: Sets environment variables for the container.
  • db: A service for our database.
    • image: postgres:13: Pulls the postgres:13 image from Docker Hub.
    • volumes: - postgres_data:/var/lib/postgresql/data: Uses a named volume to persist the database data.
• volumes: Defines named volumes used by services. postgres_data: creates a volume named postgres_data.
  
  

docker compose vs. docker-compose: A Note on Syntax

• docker-compose is the original, standalone command-line tool.
• docker compose is the newer, integrated command that is part of the Docker CLI. It was introduced with Docker v1.27.0.
  
  

Essential Docker Compose Commands

Build Your Services

• docker compose build: Builds or rebuilds the images for your services. This is necessary when you have made changes to the Dockerfile.

Start and Stop Your Containers

• docker compose up: Builds, creates, and starts all services in the docker-compose.yml file.
  
  
• docker compose down: Stops and removes all containers, networks, and volumes created by up.

• docker compose stop: Stops running containers without removing them. The containers can be restarted later.
  
  
• docker compose start: Starts containers that have been stopped.
  
  
• docker compose restart: Restarts all containers in the project.
  
  

Inspect and Manage Containers

• docker compose ps: Lists all containers in your project, showing their state, ports, and names.
  
  
• docker compose logs: Displays the logs for all services. You can also specify a service to see its individual logs (e.g. docker compose logs webserver).
  
  
• docker compose exec [service] [command]: Executes a command inside a running container (e.g. docker compose exec webserver /bin/bash).