There's a Linux Systems Group at Microsoft which has developed a number of products -- some for customers and partners and others for internal use. One of this group's deliverables is an internal Linux distribution for use within Microsoft's cloud infrastructure and edge products and services, which is known as CBL-Mariner. Microsoft has made CBL-Mariner available on GitHub recently.
InfoWorld recently published information about Microsoft's CBL-Mariner (which is where I first heard of this distribution). As InfoWorld noted, even though CBL-Mariner is a public release, it's meant for Microsoft's own use. It's a lightweight Linux distribution that could be part of Microsoft's evolving 5G/edge networking plans in its Azure for Operators unit, as InfoWorld notes. Infoworld adds that in the past, Red Hat's CoreOS used to be the preferred host for Linux containers, but it's recenttly been deprecated, so users need an alternative. By creating its own distribution for its cloud services, Microsoft can update and manage the host and container instances own its own schedule, InfoWorld adds.
Microsoft made its initial CBL-Mariner commit on GitHub four months ago. It's available under an MIT License.
I've asked Microsoft for a list of its own products and services currently using CBL-Mariner and if and how it expects Microsoft customers and partners to use CBL-Mariner. No word back so far.
Update: A spokesperson said Microsoft had nothing more to share on this topic. (Me: Hmmm.)
Update No. 2: So CBL stands for "Common Base Linux." Microsoft uses CBL-Mariner as the base Linux for containers in the Azure Stack HCI implementation of Azure Kubernetes Service. (Thanks again to Simon Bisson for the link.)
CBL-Mariner is one of a handful of Microsoft-developed Linux-related deliverables from the Linux Systems Group. Others include the Windows Subsystem for Linux version 2 (WSL2), which is part of Windows 10; an Azure-tuned Linux kernel which is designed for optimal performance as Hyper-V guests; and Integrity Policy Enforcement (IPE), a proposed Linux Security Module (LSM) from the Enterprise and Security team.
Microsoft has some other Linux-related projects it has developed in-house, including the Azure Sphere, its Linux-based microcontroller plus secure IoT service, and SONic, an open-sourced operating system for network switches;, released as part of its Open Compute Project (OCP) work.
I'm not sure whether Microsoft will be talking more about these projects next week during its day-long, virtual Open Azure Day event on November 18. I guess we'll see.