Let’s develop a simple flask application,

1. Set up the project directory: Create a new directory for your Flask project.

mkdir flask-docker-app
cd flask-docker-app

2. Create a virtual environment (optional but recommended):

python3 -m venv venv
source venv/bin/activate

3. Install Flask

pip install Flask

4. Create a simple Flask app:

In the flask-docker-app directory, create a file named app.py with the following content,

from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello, Dockerized Flask!'

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

5. Test the Flask app: Run the Flask application to ensure it’s working.

python app.py

Visit http://127.0.0.1:5000/ in your browser. You should see “Hello, Dockerized Flask!”.

Dockerize the Flask Application

1. Create a Dockerfile: In the flask-docker-app directory, create a file named Dockerfile with the following content:

# Use the official Python image from the Docker Hub
FROM python:3.9-slim

# Set the working directory in the container
WORKDIR /app

# Copy the current directory contents into the container at /app
COPY . /app

# Install any needed packages specified in requirements.txt
RUN pip install --no-cache-dir Flask

# Make port 5000 available to the world outside this container
EXPOSE 5000

# Define environment variable
ENV FLASK_APP=app.py

# Run app.py when the container launches
CMD ["python", "app.py"]

2. Create a .dockerignore file:

In the flask-docker-app directory, create a file named .dockerignore to ignore unnecessary files during the Docker build process:

venv
__pycache__
*.pyc
*.pyo

3. Build the Docker image:

In the flask-docker-app directory, run the following command to build your Docker image:

docker build -t flask-docker-app .

4. Run the Docker container:

Run the Docker container using the image you just built,

docker run -p 5000:5000 flask-docker-app

5. Access the Flask app in Docker: Visit http://localhost:5000/ in your browser. You should see “Hello, Dockerized Flask!” running in a Docker container.

You have successfully created a simple Flask application and Dockerized it. The Dockerfile allows you to package your app with its dependencies and run it in a consistent environment.