Introduction to Docker compose

Imagine a world where you can pack all of an app's dependencies and configurations into one neat, easy-to-read configuration file, ship it off to any machine, and not worry about anything else! The app runs just as it should. No more "works on my machine" excuses!

Welcome to the magical world of Docker Compose — the ultimate tool for hassle-free application deployment.

The idea behind Docker Compose

Imagine you have a brick-and-mortar store that sells clothes and you want to start selling these clothes online. For that, you need a website to showcase your designs so customers can buy what they like.

Considering your website is built using several different technologies, such as a web server, a database, and an application server. Each of these technologies has its own set of dependencies and configurations. Without Docker Compose, you have to manually set up and configure each of these technologies on each machine that runs your website.

But with Docker Compose you can pack all the dependencies and configurations in one single configuration file. When you run this file, installation and configuration of these technologies will happen automatically. This file creates a standalone environment for your website to run on any device regardless of the underlying infrastructure. This ultimately saves time and resources for your business.

Docker Compose

Docker Compose is a tool that can define and run multi-container docker applications. It uses a YAML file called docker-compose.yml to define the configuration for your application's services, networks, and volumes. This file can then be used to spin up all of the containers in the application with a single command — docker compose up. Similarly, you can use the docker compose down command to stop and remove the containers created by Docker Compose.

In addition to managing all the dependencies between your application's services, Docker Compose can also help you scale your services up or down as needed. For example, if your web service is receiving a lot of traffic, you can use Docker Compose to easily scale it up by adding more containers.

Compose example

Let's dive into an example to clarify how docker-compose works. Don't worry if you are not familiar with the technologies like Nginx and Postgres shown in this example. The important thing is that you can handle several containers at once with Docker Compose, so let's dive in and have some fun!

The fun part is that you already have a clothing business. A website is the only thing required to make your business reach millions of customers. You will use existing technologies to deploy and create your website, like Nginx for the web server and Postgres for the database.

version: '3'
services:
  web:
    image: nginx
    ports:
      - "8020:80"
    volumes:
      - ./web:/usr/share/nginx/html
    db:
      image: postgres
      environment:
        POSTGRES_USER: admin
        POSTGRES_PASSWORD: admin
        POSTGRES_DB: test_db
    app:
      image: my-custom-website
      environment:
        DATABASE_URL: postgres://admin:admin@db:4321/test_db
        depends_on:
          - db

The services section of the docker-compose.yml file contains all the components for the deployment of your website. The web section contains the web server configurations, the db section contains the database configurations and finally, the app section contains your custom build website.

This docker-compose.yml file will spin up your containers using the docker compose up command. Now, you are ready to publish designs that can reach millions.

Conclusion

To sum up, here are some key points to remember:

• Docker Compose is a tool to deploy and manage multi-container applications.
• The "docker-compose.yml" file contains all the dependencies and configurations of the whole application stack.
• By using the docker compose up command, all the containers can be spun up.
• Docker Compose eliminates the need to manually configure each service on every device.
• Docker Compose can be used to deploy or manage both simple and complex applications.
• It saves time and resources by eliminating the need for manual configuration.