✨ Add ValidatingAdmissionPolicy to enforce package uniqueness acros…

…s `ClusterExtension` (#774)

* Add `ValidatingAdmissionPolicy`

To enforce package uniqueness across `ClusterExtension`

Signed-off-by: Mikalai Radchuk <mradchuk@redhat.com>

* Kustomize `ValidatingAdmissionPolicyBinding`

This is a workaround for kustomize issue where it does not prefix
`ValidatingAdmissionPolicy`'s name in `ValidatingAdmissionPolicyBinding`'s
field `spec.policyName`. This results in manifests which can still be
applied to a cluster, but the policy will not be working due to
broken policy binding.

These APIs are now stable in 1.30 so one might expect that Kustomize
will eventually support these by default. If this happens - we will
be able to remove this change.

Signed-off-by: Mikalai Radchuk <mradchuk@redhat.com>

---------

Signed-off-by: Mikalai Radchuk <mradchuk@redhat.com>

config/admission/admission.yaml

@@ -0,0 +1,37 @@
+apiVersion: admissionregistration.k8s.io/v1beta1
+kind: ValidatingAdmissionPolicy
+metadata:
+  name: "clusterextensions-package-uniqueness"
+spec:
+  failurePolicy: Fail
+  paramKind:
+    apiVersion: olm.operatorframework.io/v1alpha1
+    kind: ClusterExtension
+  matchConstraints:
+    resourceRules:
+    - apiGroups:   ["olm.operatorframework.io"]
+      apiVersions: ["v1alpha1"]
+      operations:  ["CREATE", "UPDATE"]
+      resources:   ["clusterextensions"]
+  matchConditions:
+    # Only apply the policy when the request operation is CREATE
+    # or when the package is being changed
+    - name: 'only-create-or-package-change'
+      expression: request.operation == 'CREATE' || oldObject.spec.packageName != object.spec.packageName
+  validations:
+    - expression: object.spec.packageName != params.spec.packageName
+      messageExpression: "'Package \"' + string(object.spec.packageName) + '\" is already installed via ClusterExtension \"' +  string(params.metadata.name) + '\"'"
+      reason: Invalid
+
+---
+
+apiVersion: admissionregistration.k8s.io/v1beta1
+kind: ValidatingAdmissionPolicyBinding
+metadata:
+  name: "clusterextensions-package-uniqueness-binding"
+spec:
+  policyName: "clusterextensions-package-uniqueness"
+  validationActions: [Deny]
+  paramRef:
+    parameterNotFoundAction: Allow
+    selector: {}

config/admission/kustomization.yaml

@@ -0,0 +1,5 @@
+configurations:
+- kustomizeconfig.yaml
+
+resources:
+- admission.yaml

config/admission/kustomizeconfig.yaml

@@ -0,0 +1,9 @@
+# This file is for teaching kustomize how to substitute name in ValidatingAdmissionPolicyBinding
+# This might become obsolete depending on the outcome of https://github.com/kubernetes-sigs/kustomize/issues/5674
+nameReference:
+- kind: ValidatingAdmissionPolicy
+  group: admissionregistration.k8s.io
+  fieldSpecs:
+  - kind: ValidatingAdmissionPolicyBinding
+    group: admissionregistration.k8s.io
+    path: spec/policyName

config/default/kustomization.yaml

@@ -16,6 +16,7 @@ namePrefix: operator-controller-
 
 resources:
 - ../crd
+- ../admission
 - ../rbac
 - ../manager
 # [WEBHOOK] To enable webhook, uncomment all the sections with [WEBHOOK] prefix including the one in