Docker containerization in Flask - Mini Project: Build & Apply

Docker containerization

📖 Scenario: You are building a simple Flask web app that shows a welcome message. You want to package this app inside a Docker container so it can run anywhere easily.

🎯 Goal: Create a basic Flask app, add a Dockerfile to containerize it, and configure the container to run the app.

📋 What You'll Learn

Create a Flask app with one route that returns 'Hello from Flask in Docker!'

Create a Dockerfile that uses the official Python image

Install Flask inside the Docker container

Set the container to run the Flask app on port 5000

💡 Why This Matters

🌍 Real World

Docker lets developers package apps with all needed parts so they run the same anywhere. This is useful for sharing apps or deploying to servers.

💼 Career

Many software jobs require containerizing apps with Docker to simplify deployment and scaling in cloud or production environments.

1

Create the Flask app

Create a file called app.py with a Flask app. Import Flask from flask, create an app variable called app, and add a route / that returns the string 'Hello from Flask in Docker!'.

Flask

# Your code here
from flask import Flask
app = Flask(__name__)

# Define route here

Need a hint?

Remember to import Flask, create the app, and use @app.route('/') to define the home page.

2

Add a Dockerfile

Create a file called Dockerfile. Start with the base image python:3.12-slim. Set the working directory to /app. Copy app.py into the container.

Flask

from flask import Flask
app = Flask(__name__)

@app.route('/')
def home():
    return 'Hello from Flask in Docker!'

# Your Dockerfile content here

Need a hint?

Use FROM python:3.12-slim to start. Then set WORKDIR /app and copy app.py into it.

3

Install Flask and expose port

In the Dockerfile, add a line to install Flask using pip. Also, expose port 5000 for the Flask app.

Flask

# Dockerfile
FROM python:3.12-slim
WORKDIR /app
COPY app.py /app/
# Install Flask and expose port 5000

Need a hint?

Use RUN pip install flask to install Flask. Use EXPOSE 5000 to open the port.

4

Set the container command to run the app

In the Dockerfile, add a CMD instruction to run the Flask app with python. Use app.py and set the host to 0.0.0.0 and port to 5000 so it listens outside the container.

Flask

# Dockerfile
FROM python:3.12-slim
WORKDIR /app
COPY app.py /app/
RUN pip install flask
EXPOSE 5000
# Add CMD to run the app

Need a hint?

Use CMD ["python", "-m", "flask", "run", "--host=0.0.0.0", "--port=5000"] to start the app inside the container.