Shadow Copies in Docker Builds

One more issue that comes from internet access of Docker build is Shadow copies aka redundant files that are not cleaned after new versions of packages are installed.

For example

FROM ubuntu:20.04
RUN apt-get update && apt-get upgrade -y
RUN apt-get install -y some-package

Remind that the Docker build creates a separate layer for each RUN statement. Referring to the above Dockerfile, we can simply explain it as follows.

• The base layer is Ubuntu
• The second layer contains every file that is updated by apt-get upgrade.
• The third layer contains new packages

Clearly, the upgrade happens at the second layer without affecting the base layer. This means that new versions of packages are installed without removing old versions of files that are no longer used.

This issue makes the size of the image increase unnecessarily. We can resolve this by Multistage builds also.

But why do we not resolve all the above issues from its root cause?

References

Understanding the image layers. (n.d.). Docker Docs. Retrieved August 2, 2024, from https://docs.docker.com/guides/docker-concepts/building-images/understanding-image-layers/