What is the difference between ARG and ENV variables in a Dockerfile and how are they used?

In a Dockerfile, the variables ARG and ENV serve different purposes:

• ARG — these are variables available only during the image build process. They can be set during build with docker build --build-arg. After the build, they are not stored in the image.

• ENV — these are environment variables that are stored in the image and available during container runtime.

Example usage:

ARG VERSION=1.0
FROM python:${VERSION}

ENV APP_ENV=production

Here, VERSION sets the Python version at build time, and APP_ENV will be available inside the container when it runs.

Summary:

• ARG — for build parameters, not stored in the final image.
• ENV — for environment variables, available in the container after startup.