Annotate Base Images

apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: annotate-base-images
  annotations:
    policies.kyverno.io/title: Annotate Base Images
    policies.kyverno.io/category: Other
    policies.kyverno.io/severity: medium
    pod-policies.kyverno.io/autogen-controllers: none
    kyverno.io/kyverno-version: 1.7.0
    policies.kyverno.io/minversion: 1.7.0
    kyverno.io/kubernetes-version: "1.23"
    policies.kyverno.io/subject: Pod
    policies.kyverno.io/description: A base image used to construct a container image is not accessible by any Kubernetes component and not a field in a Pod spec as it must be fetched from a registry. Having this information available in the resource referencing the containers helps to provide a clearer understanding of its contents. This policy adds an annotation to a Pod or its controllers with the base image used for each container if present in an OCI annotation.
spec:
  rules:
    - name: mutate-base-image
      match:
        any:
          - resources:
              kinds:
                - Pod
      preconditions:
        all:
          - key: "{{request.operation || 'BACKGROUND'}}"
            operator: NotEquals
            value: DELETE
      mutate:
        foreach:
          - list: request.object.spec.containers
            context:
              - name: imageData
                imageRegistry:
                  reference: "{{ element.image }}"
              - name: basename
                variable:
                  jmesPath: imageData.manifest.annotations."org.opencontainers.image.base.name"
                  default: ""
            patchesJson6902: |-
              - path: "/metadata/annotations/kyverno.io~1baseimages{{elementIndex}}"
                op: add
                value: "{{basename}}"