$SUBJECT says it all: what is the minimum OBS version that's able to consume zstd compressed preinstallimages?
I have the feeling that released versions are not able to use that. But as soon as zstd is installed on the worker, it compresses preinstallimages with zstd.
Background: I'm providing aarch64 workers to pmbs. In order to tune the rebuild times, I have configured preinstallimage-base (only with bash in it) for aarch64 and armv7l. Everything worked well.
Today, I see that preinstallimages are no longer used. Investigating, I found that they are compressed with zstd now instead of gzip as they were before. Thus I guess that this is the reason for the regression.
I have now uninstalled (rpm -e --nodeps) zstd and locked it in zypper, preinstallimage rebuild is triggered, and.... .... the next package is using the preinstallimage again.
If this was my OBS instance, I'd just patch zstd out of obs-build, but I do not have access to the OBS server. So please make sure that the preinstallimage stay compatible to older OBS installations :-)