Centos 8 feature branch can't currently build because dnf by default expects module data to be included in repo data. A good link explaining modularity is here     https://docs.fedoraproject.org/en-US/modularity/ It appears to be a way to groups of packages, and to support multiple versions of the package group from a common base os. e.g. They are likely concurrently supporting python2 and python3 through modularity.  The build tooling described to support modularity is entirely centered around a fedora hosted build service.  My limited exploration of the subject has not yet found a way to build independently of the fedory build service.  CentOS specific documentation is also something wasn't able to find quickly. Does StarlingX need to support modularity?  This needs to be considered at multiple stages. 1) CENGN Mirroring.    CENGN probably needs to support modularity in it's mirroring process before any consideration of supporting modularity in the rest of the build process can be considered. 2) Download phase.    Our downloads are currently driven by 'lst' files that state specific versions of a packages.  We don't use non-versioned packages, nor meta-packages, nor capabilities.  Modularity seems like just another way to map an abstraction to a set of packages, and doesn't allow us to control with specificity which versions of those packages we take.  If we wish to retain that level of control going forward, modularity doesn't help us download the packages we want 3) Build phase    generate-centos-repo.sh generates a single repo from all the carefully selected rpms that we have downloaded.  At this stage, I see no need to support modularity whatsoever. Fu Yong's update tries to support modularity within the Centos 8 feature branch ...    https://review.opendev.org/c/starlingx/root/+/739883    It appears to be re-introducing modularity at stage 3, ignoring stages 1 and 2.  It is using a modules.yaml of unknown origin. It names package we don't have. For packages that we do have, it would have to be kept in sync with our lst files. Keeping up with packages we build for ourselves is a whole other matter.  It does not live in stx-tools.  And at the end of the day, we don't need it to build the iso beyond telling dnf to not fail of module data is not found. My proposed updates to master branch to support building Centos 7 based distro from a Centos 8 (or 7) build environment ...    https://review.opendev.org/c/starlingx/root/+/762701    https://review.opendev.org/c/starlingx/tools/+/762700    My approach is to not even attempt to support modularity at this time.  We don't need it.  We can explore supporting it at a later time.