PG_MAJOR missing from most Docker images

[Javex]

I'm not 100% sure if you'd consider this a bug or something that was only working accidentally: Some images contain variables like PG_MAJOR, for example the 17.5 tag does. However, others, like 17.5-standard-bookworm do not. It's a nice variable to rely on when adding more custom extension in my own build process, but they're missing on the bookworm image I find myself needing for the VectorChord extension.

% docker run --rm --entrypoint bash ghcr.io/cloudnative-pg/postgresql:17.5 -c 'env | grep PG_MAJOR'
PG_MAJOR=17
% docker run --rm --entrypoint bash ghcr.io/cloudnative-pg/postgresql:17.5-standard-bullseye -c 'env | grep PG_MAJOR'
% docker run --rm --entrypoint bash ghcr.io/cloudnative-pg/postgresql:17.5-standard-bookworm -c 'env | grep PG_MAJOR'
% docker run --rm --entrypoint bash ghcr.io/cloudnative-pg/postgresql:17.5-minimal-bullseye -c 'env | grep PG_MAJOR'

Only the first command produces this output, the others don't have that variable.

[dosubot]

Hi @Javex! I'm Dosu and I’m helping the postgres-containers team.

The absence of the PG_MAJOR environment variable in certain image variants (like -standard and -minimal) is not intentional—it's an inconsistency in how the Dockerfiles and build scripts are structured. Some images set PG_MAJOR explicitly, while others (especially those inheriting from official postgres images or using different templates) do not, even though they reference it in scripts or extension installs. There’s no documentation or comment indicating this is by design, so it’s best considered an oversight or bug in the templating/build process rather than a deliberate choice. If you need PG_MAJOR in your own builds, you can set it manually in your Dockerfile with ENV PG_MAJOR=17 (or the relevant version). It’s also worth keeping an eye on future image updates, as these kinds of inconsistencies are often addressed over time.
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[sxd]

Hi @Javex

It's not like Dosu said :P, it's intentional, we don't need that environment variable, it was something that arrived from the base image used at that time, those images are on their way to being deprecated and shouldn't be used anymore.

The new process you can overwrite the bake file on this repo and from there you'll have the PG_MAJOR version as an ARG inside the build process.

Regards!

[Javex]

Hey @sxd thanks for the quick reply. I arrived at this process by reading https://cloudnative-pg.io/blog/creating-container-images/ (looks like you wrote it, thanks!). Is there a similar post for the new method by any chance? I'm not familiar with the "bake" file so if there's a guide that would be awesome, but I understand if not!

Will using the FROM method break under this new build process at some point? For now I'm grepping out the major version from postgresql --version which seems to work...

[sxd]

@Javex yeah I have to create another blog post that shows the inherent process of a bake file to do that, is on my TODO list =(

[sxd]

@Javex stay tuned I'm writing something quick, if you can then review the steps and everything will be amazing :D

[sxd]

@Javex can you take a review into the commands y contents here please? cloudnative-pg/cloudnative-pg.github.io#314