Docker Compose Basics

Why

• configure relationships between containers
• save our docker container run settings in easy-to-read file
• create one-liner developer environment startups

  Components

  Comprised of 2 separate but related things

  1. YAML-formatted file that describes our solution options for:
  • containers
  • networks
  • volumes 2. A CLI tool docker-compose used for local dev/test automation with those YAML files

    docker-compose.yml

• Compose YAML format has it’s own versions: 1, 2, 2.1, 3, 3.1
• YAML file can be used with docker-compose command for local docker automation or..
• With docker directly in production with Swarm (as of v1.13)
• docker-compose --help
• docker-compose.yml is default filename, but any can be used with docker-compose -f

Template

version: '3.1'  # if no version is specificed then v1 is assumed. Recommend v2 minimum

services:  # containers. same as docker run
  servicename: # a friendly name. this is also DNS name inside network
    image: # Optional if you use build:
    command: # Optional, replace the default CMD specified by the image
    environment: # Optional, same as -e in docker run
    volumes: # Optional, same as -v in docker run
  servicename2:

volumes: # Optional, same as docker volume create

networks: # Optional, same as docker network create

Example 1

This create a Jekyll service.

version: '2'

# same as 
# docker run -p 80:4000 -v $(pwd):/site bretfisher/jekyll-serve

services:
  jekyll:
    image: bretfisher/jekyll-serve
    volumes:
      - .:/site
    ports:
      - '80:4000'

Example 2

This creates a wordpress service.

version: '2'

services:

  wordpress:
    image: wordpress
    ports:
      - 8080:80
    environment:
      WORDPRESS_DB_HOST: mysql
      WORDPRESS_DB_NAME: wordpress
      WORDPRESS_DB_USER: example
      WORDPRESS_DB_PASSWORD: examplePW
    volumes:
      - ./wordpress-data:/var/www/html

  mysql:
    image: mariadb
    environment:
      MYSQL_ROOT_PASSWORD: examplerootPW
      MYSQL_DATABASE: wordpress
      MYSQL_USER: example
      MYSQL_PASSWORD: examplePW
    volumes:
      - mysql-data:/var/lib/mysql

volumes:
  mysql-data:
	

Useful Links

• docker-compose.yml sample for Ghost (A web log) with load-balanced MySQL
• Compose file version 3 reference

  Docker Compose CLI

• CLI tool comes with Docker for Windows/Mac, but separate download for Linux
• Not a production-grade tool but ideal for local development and test
• Two most common commands are
  • docker-compose up # setup volumes/networks and start all containers
  • docker-compose down # stop all containers and remove cont/vol/net
• If all your projects had a Dockerfile and docker-compose.yml then “new developer onboarding” would be:
  • git clone github.com/some/software
  • docker-compose up

Demo

Clone https://github.com/BretFisher/udemy-docker-mastery/tree/master/compose-sample-2 docker-compose up for running in the foreground docker-compose up -d for running in the background docker-compose logs to see the log docker-compose ps to see list of containers docker-compose top to see list of processes docker-compose down to stop and remove the service

Assignment: Writing A Compose File

• Build a basic compose file for a Drupal content management system website. Docker Hub is your friend
• Use the drupal image along with the postgres image
• Use ports to expose Drupal on 8080 so you can localhost:8080
• Be sure to set POSTGRES_PASSWORD for postgres
• Walk though Drupal setup via browser
• Tip: Drupal assumes DB is localhost, but it’s service name
• Extra Credit: Use volumes to store Drupal unique data

Answer

version: '2'

services: 
  drupal:
    image: drupal
    ports: 
      - 8080:80
    volumes: 
      - drupal-modules:/var/www/html/modules
      - drupal-profiles:/var/www/html/profiles
      - drupal-sites:/var/www/html/sites
      - drupal-themes:/var/www/html/themes
  postgres:
    image: postgres
    environment: 
      - POSTGRES_PASSWORD=yourpasswd

volumes: 
  drupal-modules:
  drupal-profiles:
  drupal-sites:
  drupal-themes: