Hot reloading with bind mounts in Docker - Mini Project: Build & Apply

Hot Reloading with Bind Mounts in Docker

📖 Scenario: You are developing a simple web application using Docker. You want to see your code changes immediately without rebuilding the Docker image every time. This is called hot reloading.To achieve this, you will use a bind mount to link your local code folder to the container's code folder.

🎯 Goal: Build a Docker setup that uses a bind mount to enable hot reloading of your application code inside the container.

📋 What You'll Learn

Create a Dockerfile with a basic web server setup

Create a docker-compose.yml file with a bind mount from local code to container

Run the container so that code changes on the host reflect immediately inside the container

Print the container logs to verify hot reloading

💡 Why This Matters

🌍 Real World

Developers often want to see their code changes immediately without rebuilding containers. Bind mounts let the container use local code files directly, enabling fast development cycles.

💼 Career

Understanding hot reloading with Docker bind mounts is essential for DevOps roles to improve developer productivity and streamline containerized application development.

1

Create a simple Dockerfile for a Python web server

Create a file named Dockerfile with these exact lines to set up a Python 3.12 environment and copy the app.py file into the container's /app folder:

Docker

# Your code here

Need a hint?

Use the official Python 3.12 slim image. Set working directory to /app. Copy app.py from your local folder to the container. Set the command to run python app.py.

2

Create a docker-compose.yml with a bind mount for hot reloading

Create a file named docker-compose.yml with a service called web that uses the current directory as a bind mount to /app inside the container. Use the Dockerfile you created and expose port 8000:8000.

Docker

FROM python:3.12-slim
RUN pip install flask
WORKDIR /app
COPY app.py /app/app.py
CMD ["python", "app.py"]

# Your code here

Need a hint?

Use volumes to bind mount the current folder . to /app inside the container. This lets the container see your local code changes immediately.

3

Create a simple Python web app that reloads on code change

Create a file named app.py with a simple Flask web server that runs on port 8000 and prints Hello, World!. Use the debug=True option to enable hot reloading.

Docker

FROM python:3.12-slim
RUN pip install flask
WORKDIR /app
COPY app.py /app/app.py
CMD ["python", "app.py"]

version: '3.8'
services:
  web:
    build: .
    ports:
      - "8000:8000"
    volumes:
      - .:/app

# Your code here

Need a hint?

Use Flask to create a web server. The debug=True option enables hot reloading inside the container.

4

Run the container and verify hot reloading

Run docker-compose up in your terminal to start the container. Then, open http://localhost:8000 in your browser. Change the text in app.py from Hello, World! to Hello, Docker! and save. Refresh the browser to see the updated text. Finally, print "Hot reloading works!" in your Python code and run it.

Docker

FROM python:3.12-slim
RUN pip install flask
WORKDIR /app
COPY app.py /app/app.py
CMD ["python", "app.py"]

version: '3.8'
services:
  web:
    build: .
    ports:
      - "8000:8000"
    volumes:
      - .:/app

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello():
    return "Hello, World!"

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=8000, debug=True)

# Add a print statement below to confirm hot reloading
# Your code here

Need a hint?

Use print("Hot reloading works!") inside the if __name__ == '__main__': block to confirm the app runs and reloads.