Docker for DevOps Engineers (Day16)

Hey Everyone!

In our previous discussion, we covered Docker projects for DevOps Engineers. If you haven’t read it yet, you can check it out [here].

Today, we will delve into a Docker for DevOps Engineers(Day16). Previously we deployed a simple Todo Application made using Django. Today we will be doing that with the help of docker compose.

What is docker-compose?

Docker Compose is a tool for running multi-container Docker applications. It enables the configuration of an application, including services, networks, and volumes, using a YAML file. This file simplifies the listing of services for complex applications in a single file, which is particularly useful when working with complex applications with multiple containers running simultaneously.

Task-1: Using docker-compose.yml

The docker-compose.yml file is used to define and run multi-container Docker applications. Here’s a breakdown of how to use it to set up environments, configure services, link containers, and use environment variables.

Understanding a simple docker-compose.yml file. Consider the following example.

Sample docker-compose.yml File

version: "3.3"
services:
  web:
    image: nginx:latest
    ports:
      - "80:80"
  db:
    image: mysql:latest
    ports:
      - "3306:3306"
    environment:
      - MYSQL_ROOT_PASSWORD=test@123

Key Elements

1. Version: Specifies the version of the Compose file format.
2. Services: Defines the services that make up your app.
3. Service Configuration:

• web: Uses the nginx:latest image and maps port 80 on the host to port 80 in the container.
• db: Uses the mysql:latest image, maps port 3306, and sets the MySQL root password via an environment variable.

Running the Compose File

1. Create a docker-compose.yml file with the content provided above.
2. Navigate to the directory containing the docker-compose.yml file.
3. Run docker-compose up to start the services defined in the file.

Install Docker and Docker Compose (if not already installed):

• For Docker:

sudo apt-get update 
sudo apt-get install docker-ce docker-ce-cli containerd.io

• For 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
sudo chmod +x /usr/local/bin/docker-compose

Create a docker-compose.yml file:

• Open a terminal and create a directory for your project:

mkdir my_project 
cd my_project

• Create the docker-compose.yml file using a text editor:

nano docker-compose.yml

• Copy and paste the following content into the file:

version: "3.3"
services:
  web:
    image: nginx:latest
    ports:
      - "81:81"
  db:
    image: mysql:latest
    ports:
      - "3307:3306"
    environment:
      - MYSQL_ROOT_PASSWORD=test@123

• Save and exit the text editor (Ctrl+X, Y, Enter in nano).
• Note the change for the db service port mapping (3307:3306 instead of 3307:3307), assuming MySQL default port is 3306.

Run the Docker Compose File:

• In the same directory where the docker-compose.yml file is located, run:

docker-compose up

• This command will pull the necessary images and start the containers.

Access the Services:

• Open a web browser and go to http://localhost to see the Nginx welcome page.
• The MySQL database will be running, accessible on port 3306.
• Check if your docker-compose.yml has the correct ports and try to access http://localhost:81/

Task-2: Pulling and Running a Docker Image

Install Docker (if not already installed):

sudo apt-get update 
sudo apt-get install docker-ce docker-ce-cli containerd.io

Add User to the Docker Group:

• Add your user to the Docker group to run Docker commands without sudo:

sudo usermod -aG docker $USER sudo reboot

• After the machine reboots, you can run Docker commands without sudo.

Pull an Image from Docker Hub:

• Open a terminal and pull the Nginx image:

docker pull nginx:latest

Run the Container:

• Start the container:

docker run -d --name my_nginx nginx:latest

• This will run the Nginx container in detached mode.

Inspect the Container:

• Get detailed information about the container:

docker inspect my_nginx

View Container Logs:

• Check the logs of the running container:

docker logs my_nginx

Stop and Start the Container:

• Stop the container:

docker stop my_nginx

• Start the container again:

docker start my_nginx

Remove the Container:

• Once you’re done with the container, remove it:

docker rm -f my_nginx

By following these steps, you will successfully complete both tasks. If you encounter any issues, feel free to ask for further assistance.

Running Docker Commands without sudo

Add Your User to the Docker Group:

sudo usermod -aG docker $USER

Reboot Your Machine:

sudo reboot

After rebooting, you should be able to run Docker commands without sudo.

This is how we deploy multi-containerized applications on a web server using docker-compose.

By completing these tasks, you’ll gain a practical understanding of setting up multi-container applications using Docker Compose and managing Docker containers effectively.

Happy Learning :)