How I shrunk a Docker image by 98.8% – featuring fanotify

Some weeks ago, I did an internal presentation on Docker. During the presentation, one of the ops asked an seemingly trivial question: Is there anything like a “diet program for Docker Images” ?

You can find a couple of pretty decent common-sense powered approach on the web like removing well known cache folders, temporary files, installing all superfluous packages and flatten layers if not the full image. There is also the -slim declination of the official language images.

But, thinking at it, do we really need a full consistent base Linux install? Which files do we really need in a given image? I found a radical and pretty efficient approaches with a go binary. It was statically build, almost no external dependency. Resulting image: 6.12MB.

Whaou! Is there any chance to do something comparable, deterministic with any random application?

It turns out there could be one. The idea is simple: We could profile the image at run time one way or another to determine which files are ever accessed/opened/…, then remove all the remaining files. Hmm, sounds promising. Let’s PoC it.