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OPA Gatekeeper

Using OPA Gatekeeper to apply policy​

The following example shows how you can stop accidental deployment of kubernetes resources into the default namespace.

Installing Gatekeeper​

kubectl apply -f https://raw.githubusercontent.com/open-policy-agentgatekeeper/v3.20.1/deploy/gatekeeper.yaml

Creating a Policy Template​

apiVersion: templates.gatekeeper.sh/v1
kind: ConstraintTemplate
metadata:
  name: k8sblockdefaultnamespace
spec:
  crd:
    spec:
      names:
        kind: K8sBlockDefaultNamespace
      validation:
        openAPIV3Schema:
          type: object
          properties:
            exemptResources:
              type: array
              items:
                type: string
            exemptNamespaces:
              type: array
              items:
                type: string
  targets:
    - target: admission.k8s.gatekeeper.sh
      rego: |
        package k8sblockdefaultnamespace

        # Helpers
        ns := input.review.namespace
        kind := input.review.kind.kind
        apiGroup := input.review.kind.group

        # Violate if namespace is "default" (even when object.metadata.namespace is omitted),
        # unless resource or namespace are exempt.
        violation[{"msg": msg}] {
          ns == "default"
          msg := sprintf("Creation of %s/%s in the 'default' namespace is not allowed.", [apiGroup, kind])
        }

Creating a Policy Constraint​

apiVersion: constraints.gatekeeper.sh/v1beta1
kind: K8sBlockDefaultNamespace
metadata:
  name: block-default-namespace-resources
spec:
  match:
    kinds:
      - apiGroups: [""]
        kinds: ["Pod", "Service", "ConfigMap", "Secret"]
      - apiGroups: ["apps"]
        kinds: ["Deployment", "ReplicaSet", "DaemonSet", "StatefulSet"]
      - apiGroups: ["batch"]
        kinds: ["Job", "CronJob"]