Distroless image internals

We used a Google "distroless" image as the base image on a go application deployment in a project a while ago. I never looked into what distroless really means, but I had a guess. I'm also curious to look under the hood of a docker image if they really are just merged archives.

Recently there was a "Docker without docker" blog post in Hacker news about how simple docker (or rather, OCI) image format is. Spoiler: an image is tar archives on top of tar archives. The post has also a detailed explanation of how to pull images from a container registry. I shamelessly took the image pull script they shared and modified it a bit to pull the static distroless image from the Google container registry.

The image is only one layer, and here is how it looks like after I extracted it and removed all the root level empty directories with all directories with at least one file expanded.

It looks pretty empty to me, and I suppose that's the origin of the distroless term! :thinksmart:

I compared it to an alpine image with the GNU/Linux diff tool, and the output is enormous.

Comments

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