fix: add name validation for custom resources

This propagates the label constraints of Linode resources to their associated
CustomResourceDefinitions via the Kubernetes Validation Rules feature. When a
custom resource is created, the Kubernetes object name is validated against the
label constraints of its backing Linode resources. This allows CAPL-managed
resources to maintain a human-readable naming scheme between its Kubernetes
representation and the backing Linode implementation.

Validation rules are implemented via Kustomize JSON patches due to limitations
with Kubebuilder and Strategic Merge Patching with CRDs in Kubernetes.

See:
- https://kubernetes.io/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions/#validation-rules
- https://www.github.com/kubernetes/kubernetes/issues/74620
- https://www.github.com/kubernetes-sigs/kubebuilder/issues/1074
- https://www.github.com/kubernetes/kubernetes/issues/113223

config/crd/kustomization.yaml

@@ -35,6 +35,27 @@ patches:
 #- path: patches/cainjection_in_linodeobjectstoragebuckets.yaml
 #+kubebuilder:scaffold:crdkustomizecainjectionpatch
 
+# [VALIDATION]
+# patches here are for additional validation for each CRD
+- target:
+    group: apiextensions.k8s.io
+    version: v1
+    kind: CustomResourceDefinition
+    name: linodeclusters.infrastructure.cluster.x-k8s.io
+  path: patches/validation_in_linodeclusters.yaml
+- target:
+    group: apiextensions.k8s.io
+    version: v1
+    kind: CustomResourceDefinition
+    name: linodemachines.infrastructure.cluster.x-k8s.io
+  path: patches/validation_in_linodemachines.yaml
+- target:
+    group: apiextensions.k8s.io
+    version: v1
+    kind: CustomResourceDefinition
+    name: linodevpcs.infrastructure.cluster.x-k8s.io
+  path: patches/validation_in_linodevpcs.yaml
+
 # the following config is for teaching kustomize how to do kustomization for CRDs.
 configurations:
 - kustomizeconfig.yaml

config/crd/patches/validation_in_linodeclusters.yaml

@@ -0,0 +1,11 @@
+# The following patch adds additional constraints after the built-in name validation for the CRD
+- op: add
+  path: /spec/versions/0/schema/openAPIV3Schema/properties/metadata/properties
+  value:
+    name:
+      type: string
+      x-kubernetes-validations:
+      - rule: 3 <= size(self) && size(self) <= 32
+        message: >-
+          custom validation:
+          linode nodebalancer: labels must be between 3..32 characters

config/crd/patches/validation_in_linodemachines.yaml

@@ -0,0 +1,26 @@
+# The following patch adds additional constraints after the built-in name validation for the CRD
+- op: add
+  path: /spec/versions/0/schema/openAPIV3Schema/properties/metadata/properties
+  value:
+    name:
+      type: string
+      x-kubernetes-validations:
+      - rule: 3 <= size(self) && size(self) <= 64
+        message: >-
+          custom validation:
+          linode instance: labels must be between 3..64 characters
+      - rule: self.matches('^[[:alnum:]]([-_.[:alnum:]]+[[:alnum:]])*$')
+        message: >-
+          custom validation:
+          linode instance: labels:
+          must begin and end with an alphanumeric character,
+          may only consist of alphanumeric characters, hyphens (-), underscores (_) or periods (.),
+          cannot have two hyphens (--), underscores (__) or periods (..) in a row,
+          regex used for validation is: '^[[:alnum:]]([-_.[:alnum:]]+[[:alnum:]])*$',
+          see: https://www.linode.com/docs/api/linode-instances/#linode-create
+      # TODO: Consider combining this into the regex above to minimize time complexity
+      # See: https://github.com/google/cel-spec/blob/master/doc/langdef.md#time-complexity
+      - rule: "!(self.contains('--') || self.contains('__') || self.contains('..'))"
+        message: >-
+          custom validation:
+          linode instance: labels cannot have two hyphens (--), underscores (__) or periods (..) in a row

config/crd/patches/validation_in_linodevpcs.yaml

@@ -0,0 +1,25 @@
+# The following patch adds additional constraints after the built-in name validation for the CRD
+- op: add
+  path: /spec/versions/0/schema/openAPIV3Schema/properties/metadata/properties
+  value:
+    name:
+      type: string
+      x-kubernetes-validations:
+      - rule: 1 <= size(self) && size(self) <= 64
+        message: >-
+          custom validation:
+          linode vpc: labels must be between 3..64 characters
+      - rule: self.matches('^[-[:alnum:]]*$')
+        message: >-
+          custom validation:
+          linode vpc: labels:
+          can only contain ASCII letters, numbers, and hyphens (-),
+          cannot have two consecutive hyphens (--),
+          regex used for validation is: '^[-[:alnum:]]*$',
+          see: https://www.linode.com/docs/api/vpcs/#vpc-create
+      # TODO: Consider combining this into the regex above to minimize time complexity
+      # See: https://github.com/google/cel-spec/blob/master/doc/langdef.md#time-complexity
+      - rule: "!self.contains('--')"
+        message: >-
+          custom validation:
+          linode vpc: labels cannot have two consecutive hyphens (--)