The Kubernetes debian-base image provides a common base for Kubernetes system images that require external dependencies (such as iptables, sh, or anything that is more than a static go-binary).
This image differs from the standard debian image by removing a lot of packages and files that are generally not necessary in containers. The end result is an image that is just over 40 MB, down from 123 MB.
The image also provides a convenience script /usr/local/bin/clean-install that encapsulates the process of updating apt repositories, installing the packages, and then cleaning up unnecessary caches & logs.