[Breaking change]: .NET 9 container images no longer install zlib

[lbussell]

Description

.NET 9 container images no longer install zlib since it is no longer a dependency of the .NET Runtime.

Version

.NET 9 Preview 7

Previous behavior

In previous .NET versions, .NET container images installed the latest version of the zlib package from the Linux base image package repositories.

New behavior

.NET 9 container images no longer install zlib, and no longer update zlib in images where it is already installed from the base image.

Type of breaking change

• Binary incompatible: Existing binaries might encounter a breaking change in behavior, such as failure to load or execute, and if so, require recompilation.
• Source incompatible: When recompiled using the new SDK or component or to target the new runtime, existing source code might require source changes to compile successfully.
• Behavioral change: Existing binaries might behave differently at run time.

Reason for change

In .NET 9, the Runtime contains a statically linked version of zlib-ng. As a result, the .NET Runtime no longer has a package dependency on zlib. In order to reduce .NET container image sizes, .NET 9 container images no longer install zlib, and no longer update zlib in images where it is already installed from the base Linux image.

Recommended action

For most scenarios, no action is required. If your containerized .NET app has a direct package dependency on zlib, you should manually install it in your Dockerfile using the package manager.

Feature area

Containers

Affected APIs

No response

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Associated WorkItem - 297232