Merge pull request #1845 from mfranczy/nfd-image-compatibility

NFD image compatibility proposal

Author: k8s-ci-robot

enhancements/1845-nfd-image-compatibility/README.md

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+# KEP-1845: Image Compatibility with NFD
+
+## Summary
+
+Currently, there is no standard solution for describing container image requirements in relation to hardware or operating systems.
+Cloud-native technologies are being adopted by high-demand industries where container compatibility is critical for service performance and cluster preparation.
+This proposal introduces the concept of NFD image compatibility metadata.
+NFD features via NodeFeatureRules CRs can be effectively added to images to specify requirements for a host or operating system.
+
+The document has been prepared based on the experience and progress of the [OCI Image Compatibility working group](https://github.com/opencontainers/wg-image-compatibility/tree/main/docs/proposals).
+
+## Motivation
+
+Image compatibility metadata will help container image authors describe compatibility requirements in a standardized way.
+This metadata will be uploaded with the image to the image registry.
+As a result, container compatibility requirements will become discoverable and programmable, supporting various consumers and use cases where applications require a specific compatible environment.
+
+### Goals
+
+#### Phase 1
+
+- Use existing NFD features via the NodeFeatureRule API to describe container image requirements.
+- Create a new OCI artifact type for compatibility metadata.
+- Allow verification of node compatibilitym including nodes that are not yet part of the k8s cluster.
+- Add or extend the sources with missing features.
+
+#### Phase 2
+
+Phase 2 involves future prediction and shows the general direction.
+After the completion of Phase 1, either this document should be updated, or a new proposal should be created that considers the following points:
+
+- Update or generate pods with appropriate node selectors via a mutation webhook or a scheduler plugin.
+
+### Non-Goals
+
+- Make image compatibility a hard requirement for the NFD installation/usage.
+- Cover applications ABI compatibility.
+
+## Proposal
+
+Build a new NFD client tool with the following initial scope:
+
+- CRUD OCI artifact.
+- Validate nodes based on provided metadata.
+- Run directly on a host which is not part of the Kubernetes cluster, or run as a Kubernetes job on a Kubernetes node.
+
+### Design Details
+
+#### OCI Artifact
+
+[An OCI artifact](https://github.com/opencontainers/image-spec/blob/main/manifest.md#guidelines-for-artifact-usage) should be created to store image compatibility metadata on the image side.  
+The artifact can be connected with an image over [the subject field](https://github.com/opencontainers/distribution-spec/blob/11b8e3fba7d2d7329513d0cff53058243c334858/spec.md#pushing-manifests-with-subject).
+
+##### Manifest
+
+```json
+{
+  "schemaVersion": 2,
+  "mediaType": "application/vnd.oci.image.manifest.v1+json",
+  "artifactType": "application/vnd.k8s.nfd.image-compatibility.v1",
+  "config": {
+    "mediaType": "application/vnd.oci.empty.v1+json",
+    "digest": "sha256:44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a",
+    "size": 2
+  },
+  "layers": [
+    {
+      "mediaType": "application/vnd.k8s.nfd.image-compatibility.spec.v1+yaml",
+      "digest": "sha256:4a47f8ae4c713906618413cb9795824d09eeadf948729e213a1ba11a1e31d052",
+      "size": 1710
+    }
+  ],
+  "subject": {
+    "mediaType": "application/vnd.oci.image.manifest.v1+json",
+    "digest": "sha256:5b0bcabd1ed22e9fb1310cf6c2dec7cdef19f0ad69efa1f392e94a4333501270",
+    "size": 7682
+  },
+  "annotations": {
+    "oci.opencontainers.image.created": "2024-03-27T08:08:08Z"
+  }
+}
+```
+
+##### Artifact Payload (Schema)
+
+- **version** - *string*  
+This REQUIRED property specifies the version of the API being used.
+
+- **compatibilities** - *array of object*  
+This REQUIRED property is a list of compatibility sets.
+
+  - **rules** - *object*  
+  This REQUIRED property is a reference to the spec of [NodeFeatureRule API](https://kubernetes-sigs.github.io/node-feature-discovery/v0.16/usage/custom-resources.html#nodefeaturerule).
+  The spec makes it possible to describe image requirements using the discovered features from NFD sources.
+  For further reading, please review [the documentation](https://kubernetes-sigs.github.io/node-feature-discovery/v0.16/usage/customization-guide.html#nodefeaturerule-custom-resource).
+
+  - **weight** - *int*  
+  This OPTIONAL property specify the [node affinity weight](https://kubernetes.io/docs/concepts/scheduling-eviction/assign-pod-node/#node-affinity-weight).
+
+  - **tag** - *string*  
+  This OPTIONAL property allows grouping or dividing of compatibility sets.
+
+  - **description** - *string*  
+  This OPTIONAL property is intended for a brief description of a compatibility set.
+
+Example
+
+```yaml
+version: v1alpha1
+compatibilities:
+- tag: "prefered"
+  weight: 10
+  description: "Prefered node configuration"
+  rules:
+  - name: "kernel and cpu"
+    matchFeatures:
+    - feature: kernel.loadedmodule
+      matchExpressions:
+        vfio-pci: {op: Exists}
+    - feature: cpu.model
+      matchExpressions:
+        vendor_id: {op: In, value: ["Intel", "Amd"]}
+- tag: "fallback"
+  weight: 1
+  description: "Minimal required configuration"
+  rules:
+  - name: "cpu"
+    matchFeatures:
+    - feature: cpu.model
+      matchExpressions:
+        vendor_id: {op: In, value: ["Intel", "Amd"]}
+```
+
+##### Discovery
+
+A compatibility artifact shall be associated with either an image index or a specific image via the subject field of the OCI Image Spec.
+The Referrers API should be used to discover artifacts.
+If an image has multiple artifacts, it is up to the client to choose the correct one.
+By default, it is recommended to select the most recent artifact based on the 'created' timestamp.
+
+#### NFD client
+
+A new standalone command-line utility should be implemented for the NFD project that shares the same functionality as the [nfd kubectl plugin](https://nfd.sigs.k8s.io/usage/kubectl-plugin).
+Both clients should implemented the following commands:
+
+- `validate` -  validate a NodeFeatureRule object (implemented in kubectl plugin).
+- `test` - test a NodeFeatureRule object against a node (implemented in kubectl plugin).
+- `dryrun` - process a NodeFeatureRule file against a local NodeFeature file to dry run the rule against a node before applying it to a cluster (implemented in kubectl plugin).
+- `compat` - compatibility command with the following subcommands:
+  - `attach-spec` - create an artifact with image compatibility specification and attach to the image (initially users have to create the spec by hand).
+  - `remove-spec` - remove an artifact with image compatibility specification from the image.
+  - `validate-spec` - validate an artifact and image compatibility specification.
+  - `validate-node` - validate image compatibility against a node.
+
+### Test Plan
+
+To ensure the proper functioning of the nfd client, the following test plan should be executed:
+
+- **Unit Tests:** Write unit tests for the client.
+- **Manual e2e Tests:** Run nfd client with sample data to CRUD artifact and validate a local host.