What is a Dockerfile?

A Dockerfile is defined as a text file containing a series of instructions that Docker uses to automate the process of building a Docker image. This file outlines the steps needed to create the image, which includes specifying the base image, installing dependencies, and executing commands necessary to configure the environment within the image. By using a Dockerfile, developers can ensure that every build is consistent and reproducible, which is crucial for maintaining applications across different environments.

Each instruction in the Dockerfile corresponds to a specific step in the image-building process, allowing for efficient layer caching and optimization. This process ultimately streamlines the deployment of applications in containers, as the final images are ready to run with all configurations already set.

The other options refer to different contexts within Docker but do not accurately describe what a Dockerfile is. For example, managing container networking requires different tools and configurations than what is involved in building images, while Docker Compose deals with multi-container applications and uses a separate YAML configuration file rather than a Dockerfile. A binary file for running Docker applications does not relate to the purpose of a Dockerfile, which is specifically about defining how images are built.