Project-06: Building a Two-Tier Flask App with Docker Compose

Prerequisites

Make sure you have Docker and Docker Compose installed on your machine.

Step 1: Create Your Docker Compose File

The Docker Compose file is the backbone of our setup. It defines two services: mysql and flask-app. Here’s the file:

version: "3.9"

services:
  mysql:
    image: mysql:5.7
    container_name: mysql-container
    environment:
      MYSQL_ROOT_PASSWORD: root
      MYSQL_DATABASE: devops
      MYSQL_USER: admin
      MYSQL_PASSWORD: admin
    volumes:
      - ./mysql-data:/var/lib/mysql
      - ./message.sql:/docker-entrypoint-initdb.d/message.sql  
    networks:
      - twotier
    healthcheck:
      test: ["CMD", "mysqladmin", "ping", "-h", "localhost", "-uroot", "-proot"]
      interval: 10s
      timeout: 5s
      retries: 5
      start_period: 60s

  flask-app:
    build:
      context: .
    container_name: flaskapp-container
    ports:
      - "5000:5000"
    environment:
      MYSQL_HOST: mysql
      MYSQL_USER: root
      MYSQL_PASSWORD: root
      MYSQL_DB: devops
    depends_on:
      - mysql
    networks:
      - twotier
    restart: always
    healthcheck:
      test: ["CMD-SHELL", "curl -f http://localhost:5000/health || exit 1"]
      interval: 10s
      timeout: 5s
      retries: 5
      start_period: 30s

networks:
  twotier:

Key Components

• MySQL Service:

  • We mount mysql-data to /var/lib/mysql to ensure data persistence.

  • A health check is set up to verify that the MySQL service is ready.

• Flask App Service:

  • This service builds from a Dockerfile located in the same directory (.).

  • We expose port 5000 for Flask's default port.

  • Environment variables point to the mysql service for database connectivity.

  • MYSQL_HOST: mysql will allow your flask-app service to correctly connect to the MySQL database.

  • It depends on the mysql service, so the Flask app will only start once MySQL is healthy.

• Networks:

  • Both services are connected to a custom network called twotier for internal communication.

Step 2: Build and Run the Application

Navigate to the directory containing your docker-compose.yml file and run:

docker compose up

This command builds the Flask app image and starts the MySQL and Flask containers.

Step 3: Test and Verify

Once your services are up, you can test the application by visiting http://localhost:5000 on your browser. Check the health checks to ensure both MySQL and the Flask app are functioning correctly.

here is the link to github repo two-tier-flask-app