Python

To add a health check in a docker-compose.yml file for a Python application, follow these steps:

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Step 1: Create a Python Application

Create a simple Flask-based Python application (app.py) that runs a web server.

from flask import Flask

app = Flask(__name__)

@app.route('/health')
def health_check():
    return "OK", 200

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

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Step 2: Create a Dockerfile

A Dockerfile is needed to containerize the application.

# Use official Python image
FROM python:3.9

# Set the working directory
WORKDIR /app

# Copy application files
COPY app.py requirements.txt /app/

# Install dependencies
RUN pip install -r requirements.txt

# Expose port
EXPOSE 5000

# Command to run the application
CMD ["python", "app.py"]

In the same directory, create a requirements.txt file:

flask

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You can build image and use i another vm

docker build -t my-python-app:latest .

Step 3: Add Health Check in docker-compose.yml

Now, create a docker-compose.yml file and add the healthcheck section.

version: "3.8"

services:
  web:
    build: .               OR     image: my-python-app:latest 
    ports:
      - "5000:5000"
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost:5000/health"]
      interval: 30s
      timeout: 5s
      retries: 3
      start_period: 10s

Health Check Explanation

• test: Runs curl -f http://localhost:5000/health to check if the service responds with a 200 OK.

• interval: Runs the health check every 30 seconds.

• timeout: Health check fails if no response within 5 seconds.

• retries: If it fails 3 times consecutively, the container is marked as unhealthy.

• start_period: Waits 10 seconds before starting health checks.

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Step 4: Build and Run Containers

Run the following commands:

# Build the image
docker-compose build

# Start the containers
docker-compose up -d

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Step 5: Check Health Status

Run:

docker inspect --format='{{json .State.Health}}' <container_id>

Or list containers and check their health:

docker ps

You should see a "(healthy)" status in the output.

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Step 6: Simulate a Failing Health Check

Modify app.py to return a 500 error:

@app.route('/health')
def health_check():
    return "ERROR", 500

Rebuild and restart:

docker-compose build
docker-compose up -d
docker ps

You'll see the container marked as "(unhealthy)".

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This setup ensures your Python application is monitored inside Docker Compose! 🚀