Introduction

Welcome back to another day of the 90DaysOfDevOps challenge! Today, we're diving deep into the world of Docker Compose and Volumes. These powerful tools will help us orchestrate multi-container applications seamlessly and efficiently share data between containers.

Task 1: Docker Compose Magic

Step 1: Create a Multi-Container Docker-Compose File

To start, we'll create a docker-compose.yml file to define our multi-container setup. This example will include an application and a database container. Ensure Docker Compose is installed on your system.

version: '3'
services:

  backend:
    build:
      context: .
    ports:
      - "5000:5000"
    environment:
      MYSQL_HOST: mysql
      MYSQL_USER: admin
      MYSQL_PASSWORD: admin
      MYSQL_DB: myDb
    depends_on:
      - mysql

  mysql:
    image: mysql:5.7
    ports:
      - "3306:3306"
    environment:
      MYSQL_ROOT_PASSWORD: root
      MYSQL_DATABASE: myDb
      MYSQL_USER: admin
      MYSQL_PASSWORD: admin

Replace your-app-image and your-db-image with your actual application and database image names. This file specifies two services, app and database, with the necessary configurations.

Step 2: Docker-Compose Up and Down

Now, run the following commands to bring up and bring down your containers:

# Bring up containers in detached mode
docker-compose up -d

# View container status
docker-compose ps

# View container logs (replace 'app' with your service name)
docker-compose logs app

# Bring down containers and clean up
docker-compose down

Using the -d flag with docker-compose up starts the containers in detached mode, allowing you to continue working in the same terminal.

Task 2: Mastering Docker Volumes

Step 1: Creating and Sharing Volumes

Now, let's explore Docker Volumes and Named Volumes. Update your docker-compose.yml file to include a volume for data sharing:

version: '3'
services:

  backend:
    build:
      context: .
    ports:
      - "5000:5000"
    environment:
      MYSQL_HOST: mysql
      MYSQL_USER: admin
      MYSQL_PASSWORD: admin
      MYSQL_DB: myDb
    depends_on:
      - mysql

  mysql:
    image: mysql:5.7
    ports:
      - "3306:3306"
    environment:
      MYSQL_ROOT_PASSWORD: root
      MYSQL_DATABASE: myDb
      MYSQL_USER: admin
      MYSQL_PASSWORD: admin
    volumes:
      - ./message.sql:/docker-entrypoint-initdb.d/message.sql   # Mount sql script into container's /docker-entrypoint-initdb.d directory to get table automatically created
      - mysql-data:/var/lib/mysql  # Mount the volume for MySQL data storage

volumes:
  mysql-data:

This modification introduces two named volumes, app-data and db-data, which are mounted to specific paths in the containers.

Step 2: Verifying Data Sharing

Run the following commands to verify that the data is shared between containers:

# Bring up containers
docker-compose up -d

# Execute a command inside the 'app' container to create a file
docker exec -it your_app_container_id touch /app/data/shared_file.txt

# Execute a command inside the 'database' container to check the file's existence
docker exec -it your_db_container_id ls /var/lib/mysql/shared_file.txt

# Bring down containers
docker-compose down

Replace your_app_container_id and your_db_container_id with the actual container IDs obtained from docker-compose ps.

Step 3: Cleaning Up

After verifying the data sharing, you can clean up by removing the volumes:

# List all volumes
docker volume ls

# Remove the volumes
docker volume rm app-data db-data

Docker Compose and Volumes are essential tools for orchestrating multi-container applications and efficiently sharing data between them. Stay tuned for more DevOps adventures in the upcoming days!