Docker Compose & Yaml

Docker Compose

Docker Compose is a tool that allows you to define and manage multi-container Docker applications using a simple YAML file called docker-compose.yml. With Docker Compose, you can:

• Define Services: Specify the various services that make up your application (e.g., web server, database, cache).

• Configure Services: Set up how each service should run, including settings like ports, volumes, and environment variables.

• Manage Multi-Container Applications: Use a single command to start and stop all services, simplifying the orchestration of complex applications.

Basic Commands:

• docker-compose up: Starts the application and creates containers for each service defined in the docker-compose.yml.

• docker-compose down: Stops and removes all containers defined in the docker-compose.yml.

• docker-compose logs: Displays the logs from all containers in the application.

What is YAML?

YAML (YAML Ain’t Markup Language) is a human-readable data serialization language often used for configuration files. It is designed to be simple and easy to read, making it a popular choice for developers.

Key Features of YAML:

• Human-Readable: Easy to read and write, making it suitable for configuration files.

• Hierarchical Structure: Supports nested data structures, allowing for complex configurations.

• Data Serialization: Ideal for representing data structures such as lists and dictionaries.

File Extensions: YAML files typically have a .yml or .yaml extension.

---

We will create a project with :

• A Flask application that serves a simple web page.

• A Redis database that the Flask app will use for storing and retrieving data.

• Docker Compose to orchestrate these services.

Step-by-Step Solution

Step 1: Set Up Project Directory

• Create a project directory:

mkdir flask-redis-docker
cd flask-redis-docker

• Create subdirectories for the Flask app:

mkdir web

---

Step 2: Create Flask Application

• Create a file named app.py in the web directory:

# web/app.py

from werkzeug.urls import url_quote_plus as url_quote
from flask import Flask, jsonify
import redis
import os

app = Flask(__name__)
redis_host = os.environ.get('REDIS_HOST', 'redis')

r = redis.Redis(host=redis_host, port=6379, db=0)

@app.route('/')
def index():
    visits = r.incr('counter')
    return jsonify({'message': f'Hello, you are visitor number {visits}'})

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=5000)

• Create a requirements.txt file in the web directory:

Flask==2.2.2
redis==4.4.0
werkzeug==2.2.2

---

Step 3: Create a Dockerfile for Flask App

• Create a Dockerfile in the web directory:

# web/Dockerfile
FROM python:3.9

WORKDIR /app

COPY requirements.txt requirements.txt
RUN pip install -r requirements.txt

COPY . .

CMD ["python", "app.py"]

---

Step 4: Create Docker Compose File

• Create a docker-compose.yml file in the root directory:

version: '3.8'

services:
  web:
    build:
      context: ./web
    ports:
      - "5000:5000"
    environment:
      - REDIS_HOST=redis
    depends_on:
      - redis

  redis:
    image: redis:alpine
    ports:
      - "6379:6379"

---

Step 5: Build and Run the Application

• Navigate to the root of the project directory:

cd flask-redis-docker

• Run the following command to build and start the services:

docker-compose up --build

---

Step 6: Access the Application

• Open your web browser and go to:

http://localhost:5000

• You should see a JSON response like:

{"message": "Hello, you are visitor number 1"}

---

Step 7: Manage the Containers

• To stop the containers:

docker-compose down

• To view the logs:

docker-compose logs

• To start the containers again:

docker-compose up

---

Step 8: Remove the Containers

• To remove all containers defined in the docker-compose.yml:

docker-compose down