Some thought it would never happen. But as of Wednesday, you can run Red Hat Enterprise Linux on Microsoft’s Azure cloud, according to a Microsoft blog post.

The prospect of peaceful coexistence between Microsoft msft , long seen as the archetype of proprietary, closed-source software company, and the leading backer of the open-source Linux operating system, would have been unthinkable just years ago. After all, RHEL and Windows Server have been duking it out for years in the server operating system wars.

But Microsoft softened its stance as it moved into the cloud era. It had to. The open source model, which makes source code available to developers for examination and deployment, has become such a huge force in technology that Microsoft had to change its ways.

In the open source world, a company like Red Hat rht sells services and support for the software, which itself remains low-cost or free. Clearly, that model was anathema to companies like Microsoft, Oracle orcl , and other companies that made their money selling proprietary software in addition to charging for support and service.

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But the open source wave was too big to fight and Microsoft, especially under its new chief executive Satya Nadella, is all about making Azure a cloud for all technologies. Microsoft must, too, because it is coming from far behind in the public cloud battle and has to make up ground against market leader Amazon amzn Web Services.

At a big Meet Azure event four years ago, Microsoft featured the MySQL database, WordPress, and Ubuntu Linux—all open-source products— running on Azure. So, Microsoft Azure already supported Ubuntu and other Linux distributions, but Red Hat Enterprise Linux, which is widely adopted by businesses, was seen as the one that got away. It was a through-the-looking-glass sort of day.

On the same blog post, Microsoft said that Walmart’s wmt OneOps open-source cloud deployment tool will also run on Azure. The retail giant’s tech arm built OneOps to make it easier to move workloads to and from different cloud environments, in a bid to nix cloud lock-in.

Fortune Q&A with Microsoft CEO Satya Nadella.

Last November, Red Hat and Microsoft announced their intent to put RHEL on Azure, and as of today, customers can get the Red Hat images or sofware they need from the Azure Marketplace.

Update: This story is a bit more nuanced than first thought. A Microsoft spokeswoman said customers could already bring their own RHEL license and run the OS and other Red Hat products on Azure provided they register with Red Hat Cloud Access and build the software image needed to deploy on Azure.

This just shows what customer demand will do. As mentioned, RHEL competes fiercely with Microsoft Windows Server, but there’s been chatter for years that customers really wanted to be able to run RHEL on Azure even though they could already run it on Google goog Cloud Platform and Amazon Web Services, Azure’s two main public cloud rivals.

So the people have spoken, and their suppliers apparently listened.

This story was updated at 7:53 a.m. February 18, 2016 to reflect that users could, starting in November, bring their own RHEL licenses to run on Azure and to add that Azure now supports Walmart’s OneOps cloud deployment tool.