  Docker is becoming ubiquitous with containerization for developing and
deploying applications. Previous studies have analyzed Dockerfiles that are
used to create container images in order to better understand how to improve
Docker tooling. These studies obtain Dockerfiles using either Docker Hub or
Github. In this paper, we revisit the findings of previous studies using the
largest set of Dockerfiles known to date with over 9.4 million unique
Dockerfiles found in the World of Code infrastructure spanning from 2013-2020.
We contribute a historical view of the Dockerfile format by analyzing the
Docker engine changelogs and use the history to enhance our analysis of
Dockerfiles. We also reconfirm previous findings of a downward trend in using
OS images and an upward trend of using language images. As well, we reconfirm
that Dockerfile smell counts are slightly decreasing meaning that Dockerfile
authors are likely getting better at following best practices. Based on these
findings, it indicates that previous analyses from prior works have been
correct in many of their findings and their suggestions to build better tools
for Docker image creation are further substantiated.
