docker: how to show the diffs between 2 images

It is now 2019 and I just found a useful tool which was released in late 2017. https://opensource.googleblog.com/2017/11/container-diff-for-comparing-container-images.html

The following content is from container-diff github page:

container-diff diff <img1> <img2> --type=history  [History]
container-diff diff <img1> <img2> --type=file  [File System]
container-diff diff <img1> <img2> --type=size  [Size]
container-diff diff <img1> <img2> --type=rpm  [RPM]
container-diff diff <img1> <img2> --type=pip  [Pip]
container-diff diff <img1> <img2> --type=apt  [Apt]
container-diff diff <img1> <img2> --type=node  [Node]

You can similarly run many analyzers at once:

container-diff diff <img1> <img2> --type=history --type=apt --type=node

This one worked for me:

docker run -it e5cba87ecd29 bash -c 'find /path/to/files -type f | sort  | xargs -I{} sha512sum {}' > /tmp/dockerfiles.e5cba87ecd29.txt
docker run -it b1d19fe1a941 bash -c 'find /path/to/files -type f | sort  | xargs -I{} sha512sum {}' > /tmp/dockerfiles.b1d19fe1a941.txt
meld /tmp/dockerfiles*

Where e5cba87ecd29 and b1d19fe1a941 are images I am interested in and /path/to/files is a directory which could be "/". It lists all files, sorts it and add hash to it just in case. And meld highlights all the differences.

I suppose you could send both images' file systems to tarballs via docker export CONTAINER_ID or docker save IMAGE_ID (updated based on comments)

Then use whatever tool you like to diff the file systems - Git, Rdiff, etc.

Have a look at :

https://github.com/GoogleCloudPlatform/container-diff

This tool can diff local or remote docker images and can do so without requiring docker to be installed. It has file as well as package level "differs" (for example: apt, npm, and pip) so that you can more easily see the differences in packages that have changed between two docker images.

Disclaimer: I am a contributor to this project