Recently createrepo-c on Debian unstable was updated from 0.17.3 to 1.2.0. It introduces breaking compatibility about metadata (repodata/*).
In the previous versions, generated metadata was compressed in gz format, newer version use zst compression instead. This kills some yum client to work because old yum client can't handle newer metadata format correctly.
At least, (as far as I know) it affects on Amazon Linux 2 for example.
To keep compatibility with such a old platform, need to specify --compatibility option for createrepo-c.
