Microsoft is turning Azure Linux into a general-purpose, Fedora-based cloud distribution available to all Azure customers, while also productizing Flatcar as Azure Container Linux for immutable container hosts. "When Microsoft joined the Linux Foundation, there was this big conspiracy theory that somehow the Linux Foundation was undermining open source in partnership with Microsoft, and now you announce that you're shipping a Linux distribution," Jim Zemlin, the Linux Foundation's CEO, said in response to Microsoft's surprise announcement. "That's amazing." ZDNet reports: Until now, [Lachlan Everson, Microsoft's Principal Program Manager on Azure's open-source team] noted, "we had Azure Linux only available to third-party customers through AKS specifically, and that was Azure Linux 3.0." Going forward, this will be ACL. Everson emphasized that Azure Linux 4.0 is the culmination of years of internal usage and the evolution of the earlier Mariner distribution. "So we've been running Azure Linux for many years internally, and we got through to 3.0, and we only allowed it on as a container host on AKS. What we've done is make it a general-purpose, so this is all the learnings that we've had in the heritage of Mariner."

Under the hood, Azure Linux 4.0 is based on Fedora Linux and is delivered as an open distribution on GitHub. This code is available now. Yes, Red Hat knows that Microsoft has done this. Everson continued, "So, we made a decision to use Fedora as an upstream, so it's using RPMs in the Fedora ecosystem. Microsoft curates the packages and the supply chain to fit Azure's cloud platform." Microsoft also created "it to be purpose-built for Azure, which integrates vertically into all of our infrastructure to give you the best Azure Linux experience on Azure." While Azure Linux will ship as a VM image, Microsoft is already preparing a developer-friendly path onto Windows desktops: "And as of today, we have it as a VM image for your VM host on Azure. We're going to announce WSL images as well."

While developers will be able to run Azure Linux locally through WSL, Microsoft is not positioning it as a traditional desktop Linux. Asked whether he could run it on his laptop, Everson said: "I will be able to run it on my laptop, or what have you. Yes, on Windows 11." However, when pressed about a desktop experience, Everson was clear that there are "no plans" for a graphical environment. "It's optimized for server-side in the cloud," he said, adding that even on a developer machine, users should expect a lean environment. "Minimal packages, yeah. The idea is that we offer you a consistent experience to do your development on your machine, and that you can take your workloads as you develop them on your machine and run them with VS Code. You can run your applications on that, and know that the platform is the same that you're running on the cloud, so that you have that kind of consistency between environments."

Flatcar itself remains the upstream project, but Microsoft is packaging it for Azure customers. Everson described Flatcar as "purpose-built, immutable, secure by default, production-ready operating system, and Azure Container Linux is the productization of that, but we're still investing in the upstream Flatcar ecosystem and pulling that downstream into a productized exterior experience just for container workloads, so it's a container hosting in AKS." To underscore the immutable model, he added that "Everything's baked in, so there is no package manager. We bake the bits into the immutable, and they're in the immutable version. So Azure Container Linux is the immutable version. So you shouldn't be changing any system packages or any application packages. Anything that you need to change is customer workloads run in containers."

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