Tracing an image's parents through multiple official image builds

Image Builds
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I’m a little confused when trying to trace the different build steps which result in an official image. I suspect that I need to add caching_sha2_password support to the wordpress command-line image that I use (I may be wrong in this, but it’s the problem which started my inspection of the official image builds).

The image I’m using is tagged wordpress:cli. Looking at the wordpress official image page I see that this tag appears with other tag variants (cli-2.11.0, cli-2.11, cli-2, cli, cli-2.11.0-php8.2, cli-2.11-php8.2, cli-2-php8.2, cli-php8.2) which point to the Dockerfile at wordpress/cli/php8.2/alpine/Dockerfile at aa3c30f8c0a6a5ba0e1b26f73be802dfc8f18e4f · docker-library/wordpress · GitHub. This Dockerfile has a path of cli/php8.2/alpine/Dockerfile. It’s parent image is “FROM php:8.2-alpine”.

If I go to docker-library/php repository I can find the 8.2 directory which has four subdirectories: alpine3.20, alpine3.21, bookworm, and bullseye. Well, I know that the wp cli parent is an alpine variant, but how do I know if it’s built off of php/8.2/alpine3.20 or php/8.2/alpine3.21?

Have I made a mistake/faulty assumptions in how I trace the provenance of an image?

Thanks for taking the time to read my question.
Terrence

2

Go to the wordpress image description on Docker Hub, then to the Tags tab. Search for the tag, click on the link and you can find this for example:

https://hub.docker.com/layers/library/wordpress/cli/images/sha256-af464aba2afd9cb3a532949613e7f46ae6d022377cdbbbd2812d1fd41a509dc4

That shows the related image repositories. “php” in your case, but the tag can change, so it just shows a hash. You can expand that “php” section and see it’s base, which was “alpine” indeed.

Some time ago you would only see a hash in the first COPY or ADD layer, but now you can see the actual filenames. Like this in your case:

ADD alpine-minirootfs-3.21.3-x86.tar.gz / # buildkit

That shows the exact version, but even without this, you could start a container from the image and cat the alpine version inside.

docker run --rm -it wordpress:cli cat /etc/os-release

Output:

NAME="Alpine Linux"
ID=alpine
VERSION_ID=3.21.3
PRETTY_NAME="Alpine Linux v3.21"
HOME_URL="https://alpinelinux.org/"
BUG_REPORT_URL="https://gitlab.alpinelinux.org/alpine/aports/-/issues"
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