What is the purpose of a .dockerignore file?

The purpose of a .dockerignore file is to specify which files and directories should be ignored during the image build process. When building a Docker image, certain files, such as temporary files, source control metadata, and other unnecessary files, can be excluded from the context sent to the Docker daemon. By using a .dockerignore file, you can ensure that only the necessary files are included in the build context, thereby reducing the image size, speeding up the build process, and enhancing security by not sending sensitive information to the image.

The other options pertain to different Docker functionalities. Creating a new container involves specific Docker commands and configurations separate from defining which files to ignore during the build process. Listing available images or viewing running containers are operations that provide information about the current Docker environment but do not relate to managing the build context. Hence, the .dockerignore file plays a distinct and crucial role specifically in optimizing the image build process.