What is a Dockerfile in the context of containerization?

• A. A text document containing all the commands to build a Docker image
• B. A script executed at runtime inside the container
• C. A configuration file for Kubernetes
• D. A binary executable

Answer: (A)

A Dockerfile is a text document that contains the set of instructions to build a Docker image. It acts as a recipe for the image: you specify a base image with a directive like FROM, install software with RUN, add project files with COPY or ADD, set environment variables with ENV, and define what command runs by default with CMD or ENTRYPOINT. When you run docker build, Docker reads this file in the build context and creates the image in layers that correspond to each instruction. It’s a build-time artifact used to create images, not something that runs inside a container at runtime, and it’s distinct from Kubernetes configuration or any binary executable.