Microsoft Linux CBL-Mariner

This post is a two part series on the CBL-Mariner Linux. If you’re interested just in the installation you can skip this part and switch to Part 2.

It was a very well known fact that Microsoft and Linux doesn’t sync for many years. Gone are those days when we couldn’t even come up with Microsoft and Linux together in a sentence. Former Microsoft CEO Steve Ballmer (in)famously branded Linux “a cancer that attaches itself in an intellectual property sense to everything it touches” back in 2001. Fast forwarding to 2021, news says that Microsoft quietly released CBL on its GitHub and it’s released as open-source. Anyone can use it, build it, edit it & reuse it fulfilling the four essential freedom of Free software foundation.

Microsoft’s stance about open-source has also changed over the years. There have been signs on Microsoft embracing Linux for quite sometime. The Windows Subsystem for Linux (WSL) initially released in 2016 and later came up with a stable release WSL2 in 2019 is an evidence of that. The constant rise of cloud and edge computing has increased the dominance of Linux. Their surprising acquisition of GitHub back in 2018 was another strategic motion towards accepting OSS/FOSS model.

In this blog, we’ll discuss about Microsoft’s Linux (distro)? CBL-Mariner. IMHO it doesn’t qualify for being called as a distro. We’ll see why?

CBL-Mariner is a Linux developed by the Linux System Group at Microsoft, the team behind the WSL compatibility layer. The CBL part of its name stands for Common Base Linux. It is fully open-source & built for powering Microsoft’s Azure Edge services. Although Microsoft stated that it’s an internal distribution for managing their Edge infrastructure, the entire project is available publicly via GitHub. It’s a minimal and lightweight Linux that users can use as a container or container host. CBL-Mariner proves that Microsoft is on the right track when it comes to free software and Linux. The company that once stood steadfast against its open-source rival has seemingly come to terms with the changing reality of the IT industry. Let’s see what the future holds for this new strategy.

“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 GitHub pages

Looking into this release strategically, CBL-Mariner has similarities in concept and philosophy with Amazon Linux which is explicitly used in AWS. Microsoft might have thought in the same direction for use in Azure. Another aspect to look is that, RedHat’s CoreOS was deprecated in May 2020. CoreOS also known as Container Linux is a discontinued open-source lightweight operating system based on the Linux kernel and designed for providing infrastructure to clustered deployments, while focusing on automation, ease of application deployment, security, reliability and scalability. which was predominantly used in Microsoft Azure. This led Microsoft to look for an alternate Linux which they controls rather than from other enterprise Linux players. Having said that, we’ll wait and see the adoptability of CBL-Mariner.

Whether deployed as a container or a container host, CBL-Mariner consumes limited disk and memory resources. The lightweight characteristics of CBL-Mariner also provides faster boot times and a minimal attack surface. By focusing the features in the core image to just what is needed for our internal cloud customers there are fewer services to load, and fewer attack vectors. When security vulnerabilities arise, CBL-Mariner supports both a package-based update model and an image based update model. Leveraging the common RPM Package Manager system, CBL-Mariner makes the latest security patches and fixes available for download with the goal of fast turn-around times.

Microsoft uses it as the base Linux for containers in the Azure Stack HCI implementation of Azure Kubernetes Service. It’s also used in Azure IoT Edge to run Linux workloads.

Now, we talk explicitly on the CBL-Mariner. what are the features of it? how to install it? etc. in the part 2 of this series.

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