Day 18 Task: Docker for DevOps Engineers

Docker is an amazing tool that allows us to containerize applications, making them lightweight and portable. But when dealing with multi-container applications, managing individual containers can become tedious. This is where Docker Compose comes to the rescue!

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What is Docker Compose?

Docker Compose is a powerful tool designed to simplify the definition and management of multi-container Docker applications. Instead of manually running multiple docker run commands, we can define our entire application stack in a single docker-compose.yml file and manage everything with a few simple commands.

Why Use Docker Compose?

• Simplified Configuration: Define services, networks, and volumes in a YAML file.

• Easier Management: Start, stop, and rebuild entire applications with a single command.

• Reproducibility: Ensures consistency across development, testing, and production environments.

How Docker Compose Works

Docker Compose uses a YAML configuration file (docker-compose.yml) to define services, networks, and volumes. Once defined, all containers can be brought up or down using docker-compose up and docker-compose down commands.

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Understanding YAML

Before we dive into docker-compose.yml, let's quickly understand YAML (Yet Another Markup Language). YAML is used for configuration files because of its human-readable format. Here’s a simple example:

version: "3.8"
services:
  web:
    image: nginx:latest
    ports:
      - "8080:80"
    environment:
      - NGINX_HOST=localhost
      - NGINX_PORT=80

In this example, we define a web service using the latest Nginx image, exposing it on port 8080 of the host machine.

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Task 1: Writing a docker-compose.yml File

To get hands-on experience, create a docker-compose.yml file that sets up an environment with multiple services and environment variables. Here’s an example of running a simple web server with a database:

version: "3.8"
services:
  web:
    image: nginx:latest
    ports:
      - "8080:80"
    depends_on:
      - db
  db:
    image: mysql:5.7
    environment:
      MYSQL_ROOT_PASSWORD: example
      MYSQL_DATABASE: mydb
      MYSQL_USER: user
      MYSQL_PASSWORD: password

Running Docker Compose

Once the file is ready, execute the following command to bring up the services:

docker-compose up -d

To stop and remove the services, run:

docker-compose down

To check running services:

docker-compose ps

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Task 2: Running a Docker Container as a Non-Root User

By default, Docker requires root privileges, but it's a good practice to run containers as a non-root user.

1. Add Your User to the Docker Group

sudo usermod -aG docker $USER
reboot

2. Pull and Run a Docker Image

docker pull nginx
docker run -d --name mynginx -p 8080:80 nginx

3. Inspect the Running Container

docker ps
docker inspect mynginx

4. Check Logs

docker logs mynginx

5. Stop, Start, and Remove the Container

docker stop mynginx
docker start mynginx
docker rm -f mynginx

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Conclusion

Docker Compose is an essential tool for managing multi-container applications efficiently. With a simple YAML file, you can define, configure, and run complex applications effortlessly. Understanding docker-compose.yml and working with Docker as a non-root user will set the foundation for mastering DevOps workflows.