Module 8: Docker-Compose

What is Docker Compose 

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. To learn more about all the features of Compose, see the list of features.

Compose works in all environments: production, staging, development, testing, as well as CI workflows. You can learn more about each case in Common Use Cases.

Using Compose is basically a three-step process:

1. Define your app’s environment with a Dockerfile so it can be reproduced anywhere.

2. Define the services that make up your app in docker-compose.yml so they can be run together in an isolated environment.

3. Run docker compose up and the Docker compose command starts and runs your entire app. You can alternatively run docker-compose up using the docker-compose binary

Each of these can be considered a microservice. The more microservices you build into your environment, the more valuable it is to have each of these services in their containers. But as a developer, you should be able to jump from one container to another. This is where you can relate this example to Docker, where Docker Compose can connect different containers as a single service.

Docker Compose is used for running multiple containers as a single service. Each of the containers here run in isolation but can interact with each other when required. Docker Compose files are very easy to write in a scripting language called YAML, which is an XML-based language that stands for Yet Another Markup Language. Another great thing about Docker Compose is that users can activate all the services (containers) using a single command.

Basic Commands in Docker Compose

• Start all services: Docker Compose up
• Stop all services: Docker Compose down
• Install Docker Compose using pip: pip install -U Docker-compose
• Check the version of Docker Compose: Docker-compose-v
• Run Docker Compose file: Docker-compose up -d
• List the entire process: Docker ps
• Scale a service - Docker Compose up -d -scale
  
  

  Install Compose on Linux systems

• Use YAML files to configure application services - Docker Compose.yml
  

  1. Run this command to download the current stable release of Docker Compose:

     $ sudo curl -L "https://github.com/docker/compose/releases/download/1.29.2/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose
     

     To install a different version of Compose, substitute 1.29.2 with the version of Compose you want to use. For instructions on how to install Compose 2.2.3 on Linux, see Install Compose 2.0.0 on Linux

     If you have problems installing with curl, see Alternative Install Options tab above.

  2. Apply executable permissions to the binary:

     $ sudo chmod +x /usr/local/bin/docker-compose
     

     Note:

     If the command docker-compose fails after installation, check your path. You can also create a symbolic link to /usr/bin or any other directory in your path.

     For example:

     $ sudo ln -s /usr/local/bin/docker-compose /usr/bin/docker-compose
     

  3. Optionally, install command completion for the bash and zsh shell.

  4. Test the installation.

     $ docker-compose --version
     docker-compose version 1.29.2, build 1110ad01
     

  Hands-on

  Define the project

  1. Create an empty project directory.

     You can name the directory something easy for you to remember. This directory is the context for your application image. The directory should only contain resources to build that image.

     This project directory contains a docker-compose.yml file which is complete in itself for a good starter wordpress project.

     Tip: You can use either a .yml or .yaml extension for this file. They both work.

  2. Change into your project directory.

     For example, if you named your directory mkdir wordpress:

     $ cd wordpress/

  3. $ vi docker-compose.yml

  4. Create a docker-compose.yml file that starts your WordPress blog and a separate MySQL instance with volume mounts for data persistence:

     version: "3.9"
         
     services:
       db:
         image: mysql:5.7
         volumes:
           - db_data:/var/lib/mysql
         restart: always
         environment:
           MYSQL_ROOT_PASSWORD: somewordpress
           MYSQL_DATABASE: wordpress
           MYSQL_USER: wordpress
           MYSQL_PASSWORD: wordpress
         
       wordpress:
         depends_on:
           - db
         image: wordpress:latest
         volumes:
           - wordpress_data:/var/www/html
         ports:
           - "8000:80"
         restart: always
         environment:
           WORDPRESS_DB_HOST: db
           WORDPRESS_DB_USER: wordpress
           WORDPRESS_DB_PASSWORD: wordpress
           WORDPRESS_DB_NAME: wordpress
     volumes:
       db_data: {}
       wordpress_data: {}
     

  Notes:

  • The docker volumes db_data and wordpress_data persists updates made by WordPress to the database, as well as the installed themes and plugins. Learn more about docker volumes

  • WordPress Multisite works only on ports 80 and 443.

  Build the project

  Now, run docker-compose up -d from your project directory.

  This runs docker-compose up in detached mode, pulls the needed Docker images, and starts the wordpress and database containers, as shown in the example below.

  $ docker-compose up -d
  
  Creating network "my_wordpress_default" with the default driver
  Pulling db (mysql:5.7)...
  5.7: Pulling from library/mysql
  efd26ecc9548: Pull complete
  a3ed95caeb02: Pull complete
  <...>
  Digest: sha256:34a0aca88e85f2efa5edff1cea77cf5d3147ad93545dbec99cfe705b03c520de
  Status: Downloaded newer image for mysql:5.7
  Pulling wordpress (wordpress:latest)...
  latest: Pulling from library/wordpress
  efd26ecc9548: Already exists
  a3ed95caeb02: Pull complete
  589a9d9a7c64: Pull complete
  <...>
  Digest: sha256:ed28506ae44d5def89075fd5c01456610cd6c64006addfe5210b8c675881aff6
  Status: Downloaded newer image for wordpress:latest
  Creating my_wordpress_db_1
  Creating my_wordpress_wordpress_1
  

  Note: WordPress Multisite works only on ports 80 and/or 443. If you get an error message about binding 0.0.0.0 to port 80 or 443 (depending on which one you specified), it is likely that the port you configured for WordPress is already in use by another service.

  Bring up WordPress in a web browser

  At this point, WordPress should be running on port 8000 of your Docker Host, and you can complete the “famous five-minute installation” as a WordPress administrator.

  Note: The WordPress site is not immediately available on port 8000 because the containers are still being initialized and may take a couple of minutes before the first load.

  If you are using Docker Desktop for Mac or Docker Desktop for Windows, you can use http://localhost as the IP address, and open http://localhost:8000 in a web browser.

  

  

  Shutdown and cleanup

  The command docker-compose down removes the containers and default network, but preserves your WordPress database.

  The command docker-compose down --volumes removes the containers, default network, and the WordPress database.