An example OPA Gatekeeper policy that helps enforce a policy where a unique Ingress host is required to ensure there is no misconfiguration.


# Constraint Template

apiVersion: templates.gatekeeper.sh/v1beta1
kind: ConstraintTemplate
metadata:
  name: k8suniqueingresshost
spec:
  crd:
    spec:
      names:
        kind: K8sUniqueIngressHost
  targets:
    - target: admission.k8s.gatekeeper.sh
      rego: |
        package k8suniqueingresshost

        identical(obj, review) {
          obj.metadata.namespace == review.object.metadata.namespace
          obj.metadata.name == review.object.metadata.name
        }

        violation[{"msg": msg}] {
          input.review.kind.kind == "Ingress"
          re_match("^(extensions|networking.k8s.io)$", input.review.kind.group)
          host := input.review.object.spec.rules[_].host
          other := data.inventory.namespace[ns][otherapiversion]["Ingress"][name]
          re_match("^(extensions|networking.k8s.io)/.+$", otherapiversion)
          other.spec.rules[_].host == host
          not identical(other, input.review)
          msg := sprintf("ingress host conflicts with an existing ingress <%v>", [host])
        }
---

# Constraint

apiVersion: constraints.gatekeeper.sh/v1beta1
kind: K8sUniqueIngressHost
metadata:
  name: unique-ingress-host
spec:
  match:
    kinds:
      - apiGroups: ["extensions", "networking.k8s.io"]
        kinds: ["Ingress"]

Note

For this policy to work, you need to enable data replication as described here