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Docker Compose Cheatsheet

A comprehensive guide to Docker Compose, covering essential commands, configurations, and best practices for defining and managing multi-container Docker applications.

Basic Concepts & Setup

What is Docker Compose?

Docker Compose is a tool for defining and running multi-container Docker applications. With Compose, you use a YAML file to configure your application’s services. Then, with a single command, you create and start all the services from your configuration.

Key benefits include:

  • Simplified multi-container management.
  • Infrastructure as code.
  • Reproducible environments.

Installation

Docker Compose is now integrated into Docker Desktop. Ensure Docker Desktop is installed and running. For standalone installation (if needed):

# Example for Linux
sudo apt-get update
sudo apt-get install docker-compose-plugin

Docker Compose File (docker-compose.yml)

The docker-compose.yml file defines the services, networks, and volumes for your application. Here’s a basic structure:

version: '3.8'
services:
  web:
    image: nginx:latest
    ports:
      - "80:80"

Essential Commands

Lifecycle Management

docker compose up

Builds, (re)creates, starts, and attaches to containers for all services defined in the docker-compose.yml file.

Flags: -d (detached mode).

docker compose down

Stops and removes containers, networks, volumes, and images created by up.

docker compose start

Starts existing containers.

docker compose stop

Stops running containers without removing them.

docker compose restart

Restarts all services.

Service Interaction

docker compose ps

Lists the status of the containers.

docker compose logs

View output from the containers.

Service can be specified docker compose logs <service>.

docker compose exec

Execute a command in a running container.

Example: docker compose exec web bash

docker compose run

Run a one-off command against a service.

Example: docker compose run web python manage.py migrate

Configuration Inspection

docker compose config

Validate and view the Compose file configuration.

Useful for verifying your setup.

docker compose version

Displays the Docker Compose version.

Configuration Options

Build Configuration

Use the build directive to configure how a service is built from a Dockerfile.

version: '3.8'
services:
  web:
    build:
      context: ./web
      dockerfile: Dockerfile.dev
      args:
        NODE_ENV: development
  • context: Path to the build context (directory containing the Dockerfile).
  • dockerfile: Name of the Dockerfile (defaults to Dockerfile).
  • args: Build-time arguments.

Image Configuration

Specify a pre-built image using the image directive:

version: '3.8'
services:
  web:
    image: nginx:latest

You can also specify a private registry:

image: your-registry.com/your-image:tag

Port Mapping

Expose ports from the container to the host machine:

version: '3.8'
services:
  web:
    ports:
      - "80:80"  # host:container
      - "443:443"

Use expose to expose ports between linked services (not accessible from the host):

expose:
  - "3000"

Volumes

Share directories or volumes between the host and containers.

version: '3.8'
services:
  web:
    volumes:
      - ./app:/var/www/html  # host_path:container_path
      - data-volume:/data      # named volume

volumes:
  data-volume:

Environment Variables

Set environment variables for services.

version: '3.8'
services:
  web:
    environment:
      - DATABASE_URL=postgres://user:pass@db:5432
      - API_KEY=${API_KEY}
    env_file:
      - .env
  • environment: Define variables directly in the Compose file.
  • env_file: Load variables from one or more .env files.
  • ${VARIABLE}: Use environment variables from the host system.

Advanced Configuration

Dependencies & Health Checks

Define service dependencies and health checks to ensure proper startup order and service availability.

version: '3.8'
services:
  web:
    depends_on:
      db:
        condition: service_healthy
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost"]
      interval: 1m30s
      timeout: 10s
      retries: 3
      start_period: 40s
  • depends_on: Define service dependencies and startup order. Conditions: service_healthy, service_started.
  • healthcheck: Define how Docker determines if a service is healthy.

Networks

Create custom networks for inter-container communication.

version: '3.8'
services:
  web:
    networks: [frontend]
  db:
    networks: [frontend]

networks:
  frontend:
    driver: bridge
  • networks: Specify which networks a service belongs to.
  • driver: Network driver (e.g., bridge, overlay).

Extending Services

Use extends to share configurations between services.

version: '3.8'
services:
  web:
    extends:
      file: common-config.yml
      service: webapp
  • file: Path to the configuration file containing the base service.
  • service: Name of the service to extend.

Resource Limits

Limit the resources a container can use.

version: '3.8'
services:
  web:
    deploy:
      resources:
        limits:
          cpus: '0.5'
          memory: 512M
  • cpus: CPU limit (e.g., 0.5 for 50% of a CPU core).
  • memory: Memory limit (e.g., 512M, 1G).
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