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Docker compose brief

Are you tired by executing docker run, docker build? so are we...

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.

Using Compose is essentially 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.

A docker-compose.yml looks like this:

version: "3.9"
services:
  web:
    build: docker-containers
    ports:
      - "8000:5000"
    volumes:
      - .:/code
      - logvolume01:/var/log
    depends_on:
      - redis
  redis:
    image: redis
volumes:
  logvolume01: { }

The given Docker Compose file describes a multi-service application with two services: web and redis. Here's a breakdown of some components:

  1. version: "3.9" specifies the version of the Docker Compose syntax being used.
  2. services: begins the services section, where you define the containers for your application.
  3. web: defines a service named web. This service is built from the current directory (build: .) using a Dockerfile.
  4. volumes: defines volume mappings between the host and container.
  5. redis: defines a service named redis. This service uses the official Redis image.

Compose benefits

Using Docker Compose offers several benefits:

  • Simplified Container Orchestration: Docker Compose allows for the definition and management of multi-container applications as a single unit.
  • Reproducible Environments: Since compose is defined in a YAML file, it's easy to deploy the same environment in different machine without missing any docker run command. This ensures that the application runs consistently across different machines.
  • Automate Volumes and Networking: Docker Compose automatically creates a network for the application and assigns a unique DNS name to each service. No need to create networks and volumes.

Installation

If you already have Docker Engine and Docker CLI installed, you can install the Compose plugin from:

https://docs.docker.com/compose/install/linux/#install-using-the-repository

Introducing YAML

YAML (YAML Ain't Markup Language) is a human-readable data format commonly used for configuration files and data exchange between systems. YAMl is the cousin of JSON, by means that it uses indentation and key-value pairs to represent structured data, very similarly to JSON, by in a more clean syntax.

To prepare for working with Docker Compose, and later with Kubernetes, it is important to familiarize yourself with YAML syntax, which is the preferred syntax for writing Docker Compose files.

Find your favorite tutorial (there are hundreds YouTube videos and written tutorials) to see some YAML basic syntax (it takes no more than 20 minutes).

Try compose

In this course we will briefly introduce Docker Compose only as a stepping stone towards learning Kubernetes. Docker Compose is nice tool to get yourself familiar with the concept of container orchestration and deployment. However, Kubernetes (k8s) is way more powerful orchestration platform, which will be learnt later on in the course.

The official Docker Compose website provides good getting started tutorial with Docker Compose, explaining key concepts and demonstrating how to write a Compose file. Complete the tutorial:
https://docs.docker.com/compose/gettingstarted/

Self-check questions

Enter the interactive self-check page

Exercises

✏️ Flask, Nginx, MongoDB

Create docker-compose.yaml file for the following containers architecture:

  • The Dockerfiles of the nginx and the flask services can be found in our shared repo under nginx_flask_mongodb.
  • The mongo service should be run using the pre-built official Mongo image. The database data should be persistent.
  • The nginx and flask services should be connected to a custom bridge network called public-net-1 network.
  • In addition, the flask service and mongo should be connected to a custom bridge network called private-net-1 network.
  • The nginx should talk with flask using the flask-app hostname.
  • The flask service should talk to the mongo using the mongo hostname.