[RFC] Noble Based cflinuxfs5

toc/rfc/rfc-draft-noble-based-cflinuxfs5.md

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+# Meta
+[meta]: #meta
+- Name: Introduce cflinuxfs5 Stack Based on Ubuntu Noble (24.04)
+- Start Date: 2025-04-07
+- Author(s): @vpetrinski @plamen-bardarov
+- Status: Draft
+- RFC Pull Request: (fill in with PR link after you submit it)
+
+## Summary
+
+Introduce a new stack, `cflinuxfs5`, based on Ubuntu 24.04 LTS (Noble Numbat), to provide an up-to-date root filesystem for application workloads.
+This stack will be added alongside the current `cflinuxfs4` (Jammy-based) stack.
+
+## Problem
+
+The current `cflinuxfs4` stack is based on Ubuntu 22.04 LTS (Jammy). Support ends in 2027
+With the release of Ubuntu 24.04 LTS (Noble), newer language runtimes, system libraries, and security updates will increasingly depend on a newer base OS.
+`cflinuxfs4` does not provide forward compatibility with these updates, and long-term support planning requires us to begin adopting Noble.
+
+## Proposal
+
+### Produce a new `cflinuxfs5` stack based on Ubuntu Noble.
+It will be introduced as a parallel stack. `cflinuxfs5` will be validated against supported buildpacks and application workloads.
+The goal is to support both cflinuxfs4 and cflinuxfs5 until the end-of-life (EOL) for Jammy(cflinuxfs4).
+
+It will be based on Ubuntu 24.04 LTS (Noble) and follow the same structure, tooling, and release process as the existing `cflinuxfs4` stack process. The production of `cflinuxfs5` belongs to the App Runtime Interfaces Working Group.
+
+### Create new buildpack versions that are compatible with `cflinuxfs5`
+The creation of a new set of buildpacks that are compatible with `cflinuxfs5`. Each buildpack will be tested against the new `cflinuxfs5` rootfs and updated as needed.
+Buildpacks are expected to support both `cflinuxfs4` and `cflinuxfs5` during the transition.
+Any buildpack-specific incompatibilities with Ubuntu Noble need to be tracked and patched incrementally.
+
+## Workstream 
+### App Runtime Deployments WG
+The ARD WG will integrate the cflinuxfs5 stack into the cf-deployment project and also validate the new stack. The steps will be similar to the cflinuxfs4 adoption (see cloudfoundry/cf-deployment#989):
+
+- Integrate cflinuxfs5-release into the "update-releases" pipeline to enable automatic version updates
+- Provide an experimental ops file to integrate cflinuxfs5 and the cflinuxfs5 buildpacks (as available)
+- Run CATs against a cflinuxfs5-enabled cf-deployment
+- Promote experimental ops file (or integrate directly into cf-deployment.yml)
+- Make cflinuxfs5 the default stack (-> major cf-d release)
+- The deprecation and removal of cflinuxfs4 will happen at a later time as that stack is being supported for now.
+
+### Matrix
+| Stack       | CFLinux Base OS     | Supported Stemcells         |
+|-------------|---------------------|------------------------------|
+| cflinuxfs5  | Ubuntu Noble 24.04  | Noble and Jammy (until EOL) |