Kubernetes ValidatingAdmissionPolicy to deny short namespaces.

deny-short-namespace-names.yaml

---
apiVersion: admissionregistration.k8s.io/v1
kind: ValidatingAdmissionPolicy
metadata:
  name: deny-short-namespace-names
spec:
  failurePolicy: Deny # Deny the request if the validation fails
  matchConstraints:
    resourceRules:
    - apiGroups: [""] # "" represents the core API group for Namespaces
      apiVersions: ["v1"]
      operations: ["CREATE"] # Only apply this policy during creation
      resources: ["namespaces"]
  validations:
  - expression: "object.metadata.name.length() >= 4"
    message: "Namespace names must be at least 4 characters long."
---
apiVersion: admissionregistration.k8s.io/v1
kind: ValidatingAdmissionPolicyBinding
metadata:
  name: deny-short-namespace-names-binding
spec:
  policyName: deny-short-namespace-names
  validationActions: [Deny] # Ensure the policy actually denies the request
  matchResources: