Add Guidelines for Platforms Tested in CI (#3726)

* Add Guidelines for Platforms Tested in CI

* Apply suggestions from code review

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

* Misc edits

* Update Documentation/ci-platform-coverage-guidelines.md

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

* 'supported' clarity

* Add clarity on distro versions

* Update Documentation/ci-platform-coverage-guidelines.md

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

---------

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

Author: 3 people

Documentation/ci-platform-coverage-guidelines.md

@@ -0,0 +1,45 @@
+# Guidelines for Platforms Tested in CI
+
+This document contains the guidelines for which platforms (OS and architectures) to test in
+the source build CI.
+
+## Distro Families
+
+1. Prefer testing base distros of families over derivatives.
+1. Prioritize testing distros that source build .NET.
+1. Use CentOS Stream instead of Red Hat because it is the free alternative.
+1. Include a permutation of distros for the supported C standard library implementations
+(e.g. glibc and musl).
+1. Only test [distros that are officially supported by .NET](https://github.com/dotnet/core/blob/main/os-lifecycle-policy.md#net-supported-os-policy).
+Community supported distros will not be covered.
+
+**Note:** There will be conflicts within these guidelines.  When they occur, it is an indication
+that multiple legs will be needed. For example, Ubuntu is based on Debian. However, .NET is included
+in Ubuntu's repositories by default but not Debian's (at the time of writing). As such, it is best
+to include legs for both Ubuntu and Debian.
+
+## Distro Versions
+
+When selecting which distro versions to test the .NET version in development, it is important to take into account which distro versions will be in support at the time of the .NET release.  Don't worry about testing .NET on distro versions that will be or nearing EOL on the .NET release day.
+
+1. Latest LTS version. If the distro doesn't have an LTS notion, then test latest.
+1. Oldest version that will be in-support for the lifetime of the .NET release.
+
+## Architectures
+
+1. Amd64
+1. Arm64
+
+## Permutations
+
+It is not the intent to test every permutation of distro family, distro version, and architecture.
+Rather, smart decisions should be made to utilize resources. For example, test the oldest LTS version
+of Debian on amd64 and the latest LTS version of Ubuntu on arm64.
+
+1. CentOS Stream
+    1. Newest in support version
+    1. Oldest in support version (for the lifetime of .NET)
+1. Fedora - Newest in support version
+1. Debian - Oldest LTS version (for the lifetime of .NET)
+1. Ubuntu - Newest LTS version (arm64)
+1. Alpine - Newest in support version

Documentation/package-dependency-flow.md

@@ -42,8 +42,8 @@ ability to service the product.
 
 ## Package Versions
 
-Package dependencies that defined using 
-[Arcade's Darc patterns](https://github.com/dotnet/arcade/blob/main/Documentation/Darc.md)
+Package dependencies defined using 
+[Arcade's dependency patterns](https://github.com/dotnet/arcade/blob/main/Documentation/Darc.md)
 will get lifted dynamically during a source build if the following conditions are met:
 
 1. The dependency is declared in the Version.Details.xml file.
@@ -83,7 +83,7 @@ This reference does not have to be direct, it can be transitive.
 
 When these conditions are met during a source build, the infrastructure will scan
 the Version.Details.xml file and dynamically create two new Versions.props files
-containing updated version properties for all non-pinned dependencies.  
+containing updated version properties for all non-pinned dependencies.
 
 **PackageVersions.Previous.props:** This will contain version properties with the
 package versions from the [previous release of source build](#previous-source-built-packages).