Add breaking change for containers - default tag (#45054)

* Add breaking change for containes - default tag

* Apply suggestions from code review

Co-authored-by: Logan Bussell <[email protected]>
Co-authored-by: Matt Thalman <[email protected]>

* Update per feedback

* Fix TOC

---------

Co-authored-by: Logan Bussell <[email protected]>
Co-authored-by: Matt Thalman <[email protected]>
Co-authored-by: Cam Soper <[email protected]>

Author: 4 people

docs/core/compatibility/10.0.md

@@ -16,6 +16,12 @@ If you're migrating an app to .NET 10, the breaking changes listed here might af
 >
 > This article is a work in progress. It's not a complete list of breaking changes in .NET 10. To query breaking changes that are still pending publication, see [Issues of .NET](https://issuesof.net/?q=%20is:open%20-label:Documented%20is:issue%20(label:%22Breaking%20Change%22%20or%20label:breaking-change)%20(repo:dotnet/docs%20or%20repo:aspnet/Announcements)%20group:repo%20(label:%22:checkered_flag:%20Release:%20.NET%2010%22%20or%20label:10.0.0)%20sort:created-desc).
 
+## Containers
+
+| Title                                                                                                                      | Type of change      | Introduced version |
+|----------------------------------------------------------------------------------------------------------------------------|---------------------|--------------------|
+| [Default .NET images use Ubuntu](containers/10.0/default-images-use-ubuntu.md)                                             | Behavioral change   | Preview 1          |
+
 ## Core .NET libraries
 
 | Title                                                                                                                      | Type of change      | Introduced version |

docs/core/compatibility/containers/10.0/default-images-use-ubuntu.md

@@ -0,0 +1,47 @@
+---
+title: "Default .NET container tags now use Ubuntu"
+description: Learn about the breaking change where the default .NET container tags, like `10.0`, use Ubuntu.
+ms.date: 2/26/2025
+---
+
+# Default .NET images use Ubuntu
+
+The default Linux distro for .NET tags has been changed from Debian to Ubuntu. This applies to all .NET tags that do not explicitly specify an OS.
+
+Debian images are still produced and supported. They can be referenced using the `-trixie-slim` suffix.
+
+- `docker pull mcr.microsoft.com/dotnet/sdk:10.0-preview` - Refers to Ubuntu 24.04 "Noble Numbat"
+- `docker pull mcr.microsoft.com/dotnet/sdk:10.0-preview-noble` - Refers to Ubuntu 24.04 "Noble Numbat"
+- `docker pull mcr.microsoft.com/dotnet/sdk:10.0-preview-trixie-slim` - Refers to Debian 13 "Trixie"
+
+The same change will apply to `10.0` tags once the `-preview` suffix is removed. This change was proposed in [dotnet-docker #5709](https://github.com/dotnet/dotnet-docker/discussions/5709).
+
+## Version introduced
+
+.NET 10 Preview 1
+
+## Previous behavior
+
+.NET 9 and earlier default tags reference images based on Debian.
+
+## New behavior
+
+Default tags reference images based on Ubuntu.
+
+## Type of breaking change
+
+This change is a [behavioral change](../../categories.md#behavioral-change).
+
+## Reason for change
+
+Debian and .NET release cycles (for mainline support) are the same length, while Debian is released (and by extensions) goes out of support first. Ubuntu support periods are much longer, such that a given .NET release will go out of support before the given Ubuntu version.
+
+## Recommended action
+
+Test your application. This change is unlikely to affect users.
+
+If you prefer Debian or have a dependency on it, use a Debian specific tag, such as `10.0-preview-trixie-slim`.
+
+## Affected APIs
+
+N/A

docs/core/compatibility/toc.yml

@@ -8,6 +8,10 @@ items:
         items:
           - name: Overview
             href: 10.0.md
+          - name: Containers
+            items:
+              - name: Default .NET images use Ubuntu
+                href: containers/10.0/default-images-use-ubuntu.md
           - name: Core .NET libraries
             items:
               - name: API obsoletions with non-default diagnostic IDs
@@ -1316,6 +1320,10 @@ items:
                 href: configuration/7.0/diagnostics-config-section.md
       - name: Containers
         items:
+          - name: .NET 10
+            items:
+              - name: Default .NET images use Ubuntu
+                href: containers/10.0/default-images-use-ubuntu.md
           - name: .NET 9
             items:
               - name: Container images no longer install zlib