Microsoft Has Now Its Own Linux Distribution Builder, CBL-Mariner
"CBL-Mariner is Microsoft's internal tool to create Linux distributions. Meant to power Microsoft's own Cloud infrastructure, CBL-Mariner distributions aim to consume limited disk and memory resources, as well as offer minimal attack surface."
CBL-Mariner is in some ways related to the Photon OS Project and to Fedora, from both of which it leverages a number of SPEC files. CBL-Mariner is mostly licensed under the MIT license, with Linux contributions licensed under GPL2 and drivers coming with their own licenses.