CBL-Mariner is an RPM-based Linux platform that is security-focused and not a general purpose Linux distribution but rather catering to their various internal use-cases although CBL-Mariner is now public.
The July 2021 update of CBL-Mariner released today enables the /dev/mcelog machine check error log, adds a new Microsoft repo to images, Cronie and logrotate are added to images, SELinux is now available but not enabled by default, and various other changes to the OS images. CBl-Mariner July 2021 also has various fixes, including a number of security fixes for contained software.
More details on this monthly update to Microsoft's CBL-Mariner Linux platform can be found via GitHub .