What is the primary purpose of the EXPOSE directive in a Dockerfile?

The primary purpose of the EXPOSE directive in a Dockerfile is to document which ports the container listens on at runtime. This serves as a form of metadata that informs users of the container about the ports that are intended for interaction, such as communication with other containers or external services. While EXPOSE does not actually publish the ports or make them accessible; it acts as a declaration that can facilitate the configuration of networking between containers.

This documentation aspect is crucial for developers and operators who need to know how to interact with the running container. Furthermore, when running containers with docker run, users can specify which ports to publish using the -p or --publish option. The EXPOSE directive essentially allows for better clarity and communication regarding the container's intended network usage.

Other options may mention functionalities related to networking, command execution, or environment variables, but these do not align with the specific role of the EXPOSE directive, which centers expressly on port documentation for effective container configuration and interaction.