Microsoft rolls out Azure Linux 4.0

Microsoft said on May 18 that Azure Linux 4.0 will enter public preview on Azure Virtual Machines and that Azure Container Linux, its immutable container-focused operating system, is now generally available. The announcement came in a Microsoft Open Source Blog post tied to Open Source Summit North America 2026 and ahead of a broader rollout at Microsoft Build on June 2. (opensource.microsoft.com) Brendan Burns, Microsoft’s corporate vice president and technical fellow for Azure OSS and Cloud Native, said the products are designed as a “hardened Linux distribution” for cloud-native and AI workloads. Microsoft framed the move as part of a broader open-source and AI infrastructure push. ### What exactly did Microsoft launch this week? Microsoft’s May 18 post drew a line between two products: Azure Linux 4.0 for Azure virtual machines and Azure Container Linux for containerized environments. (opensource.microsoft.com) Burns said Azure Linux 4.0 is headed to public preview on VMs, while Azure Container Linux has reached general availability. The June 2 date matters because Microsoft said Azure Container Linux will get a broader rollout at Build. Cloud Native Now, citing Microsoft’s announcement, reported that Azure Linux 4.0 is currently available in public preview for Azure virtual machines and that Azure Container Linux is scheduled for broader rollout during Build. (opensource.microsoft.com) ### Why is Microsoft talking about Linux and AI together? Brendan Burns said “open source is the foundation for AI” and described the shift “from cloud native to AI native” as the next stage of that ecosystem. In the same post, he said Linux, Kubernetes and containers underpin modern cloud systems and AI infrastructure. (opensource.microsoft.com) Microsoft also used the announcement to show how much of its own cloud runs on Linux. Burns said more than two-thirds of customer cores in Azure run Linux, and that Microsoft 365, GitHub and OpenAI’s ChatGPT all sit on Linux foundations. ### What does Microsoft say these systems are built to do? Microsoft said Azure Linux and Azure Container Linux are meant to make the operating-system layer “secure by default, consistent across hosts and containers, and out of your way.” Burns said both products have a reduced package footprint, a transparent supply chain and consistent performance characteristics from host to container. (opensource.microsoft.com) Microsoft’s documentation for Azure Linux Container Host for AKS adds detail on that security pitch. The company says it maintains the full stack, from the Linux kernel to CVE handling, support and end-to-end validation, and that it scans included packages for vulnerabilities twice a day through the National Vulnerability Database process. (opensource.microsoft.com) ### How does this fit with Microsoft’s existing Kubernetes business? Microsoft’s Azure CLI release notes show Azure Container Linux is already part of Azure Kubernetes Service options through the `--os-sku` parameter. That places the operating system inside the company’s managed Kubernetes tooling rather than as a separate side project. AKS support pages also show Microsoft has been moving customers through Azure Linux version changes. (opensource.microsoft.com) Microsoft said Azure Linux 2.0 for AKS stopped receiving support and security updates on Nov. 30, 2025, and that node images would be removed beginning March 31, 2026, with customers told to migrate to a supported Azure Linux version or to `osSku AzureLinux3`. ### Why does owning the operating-system layer matter? (learn.microsoft.com) Cloud Native Now reported that Azure Linux 4.0 expands Microsoft’s Linux distribution beyond earlier container-focused uses into broader server workloads. The publication said Microsoft confirmed the system is built using Fedora as an upstream base, with Microsoft curating packages and supply-chain components for Azure deployments. (learn.microsoft.com) Microsoft’s own description is narrower but points the same way operationally. Burns said the goal is a Linux foundation that is consistent across hosts and containers, while Microsoft’s AKS documentation says the company is responsible for the full Azure Linux container-host stack, including security fixes and validation. (learn.microsoft.com) Microsoft said the next public milestone is June 2 at Build, when Azure Container Linux is due for broader rollout. Azure Linux 4.0, meanwhile, is entering public preview on Azure Virtual Machines, according to the company’s May 18 post. (opensource.microsoft.com) (cloudnativenow.com)