CBL-Mariner is an internal Linux distribution for Microsoft’s cloud infrastructure and edge products and services. CBL-Mariner is designed to provide a consistent platform for these devices and services and will enhance Microsoft’s ability to stay current on Linux updates. This initiative is part of Microsoft’s increasing investment in a wide range of Linux technologies, such as SONiC, Azure Sphere OS and Windows Subsystem for Linux (WSL). CBL-Mariner is being shared publicly as part of Microsoft’s commitment to Open Source and to contribute back to the Linux community. CBL-Mariner does not change our approach or commitment to any existing third-party Linux distribution offerings.

https://azure.microsoft.com/en-us/blog/announcing-the-preview-of-azure-spot-virtual-machines/