What is the purpose of creating a Dockerfile and what role does it play in application containerization?

A Dockerfile is a text file containing a set of instructions that describe how to build a Docker image for containerizing an application. It serves as a recipe that Docker follows to create an image containing all necessary dependencies, configurations, and the application itself.

Main roles of a Dockerfile:

• Automating the image build process.
• Ensuring reproducibility of the environment.
• Simplifying deployment of the application in a container.

An example of a simple Dockerfile for a Python application:

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

# Copy application files into the container
COPY . /app
WORKDIR /app

# Install dependencies
RUN pip install -r requirements.txt

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

Thus, a Dockerfile allows describing all the steps to create an isolated and ready-to-run container with the application.