When Microsoft announced in mid-June that Windows Server was moving to the same twice-yearly feature update schedule as Windows client, officials simultaneously announced the future direction for Nano Server.

I only gave the Nano Server change a brief mention in my coverage. But it’s worth more than that, given just how big it will be.

Nano Server was a new install option that Microsoft introduced with Windows Server 2016. Nano Server was meant to provide Windows Server customers the ability to run Windows Server stripped down to its smallest footprint. Nano Server was designed to be about 1/20th the size of Windows Server Core, and consisted only of the “essential” Server components (Hyper-V, Clustering, Networking, Storage, .Net, Core CLR) — and no GUI.

This is not what Nano Server will be starting this Fall, however.

Coming with this September’s feature update to Windows Server 2016 — Windows Server 1709 — Microsoft is tweaking what Nano Server is and what it will be optimized to do and not do.

Starting with the coming feature update (1709), according to Microsoft, “Nano Server will be available only as a container base OS image. You must run it as a container in a container host, such as a Server Core installation of the next release of Windows Server.”

Moving forward, says Microsoft in its documentation:

• Nano Server has been optimized for .NET Core applications.
• Nano Server is even smaller than the Windows Server 2016 version. Windows PowerShell, .NET Core, and WMI are no longer included by default, but you can include PowerShell and .NET Core container packages when building your container.
• There is no longer a servicing stack included in Nano Server.
• Microsoft publishes an updated Nano container to Docker Hub that you redeploy.
• You troubleshoot the new Nano Container by using Docker.
• You can now run Nano containers on IoT Core.

This is a big change from the way that Microsoft originally positioned Nano Server, as Petri.com’s Aidan Finn noted in a recent blog post.

Two years ago, Microsoft execs were basically saying Nano Server was the future of Windows Server. Things didn’t quite play out that way. Finn noted that because Nano Server was so completely refactored, code had to be written expressly to run on Nano Server.

But with the coming 1709 do-over, Nano Server will be focused entirely on running in containers.What this means from a deployment standpoint, Finn explains:

“Microsoft is removing all physical features from Nano Server. That means that drivers will be removed. Hyper-V will be removed. SOFS (Scale Out File Server) will be removed. Failover Clustering will be removed. In short, you will not be able to install Nano Server on a physical virtual machine. In fact, you will not be able to install Nano Server into a VHD either. There will be no virtual machine support.”

The Windows Server Insider testing program should be kicking off within the next couple of weeks, giving those involved a glimpse as to how the new Nano Server will take shape.