What is a Dockerfile and what is it used for?

A Dockerfile is a text file containing a set of instructions that describe how to build a Docker image. It is used to automate the process of creating containers with an application and its environment.

With a Dockerfile, you can:

• Define a base image (e.g., python:3.9).
• Install necessary dependencies.
• Copy the application's source code into the image.
• Execute build or configuration commands.
• Set the command that will run when the container starts.

Example of a simple Dockerfile for a Python application:

FROM python:3.9-slim
WORKDIR /app
COPY requirements.txt ./
RUN pip install -r requirements.txt
COPY . .
CMD ["python", "app.py"]

Thus, a Dockerfile allows for reproducible and convenient creation of images for running applications in containers.