kube-review

Simple command line utility to transform a provided Kubernetes resource into a Kubernetes AdmissionReview request, as sent from the Kubernetes API server when dynamic admission control (i.e. webhook) is configured.

deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
  labels:
    app: nginx
spec:
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - image: nginx
        name: nginx
        ports:
        - containerPort: 8080

Command

$ kube-review create deployment.yaml

Output

{
    "kind": "AdmissionReview",
    "apiVersion": "admission.k8s.io/v1",
    "request": {
        "uid": "2024ee9c-c374-413c-838d-e62bcb4826be",
        "kind": {
            "group": "apps",
            "version": "v1",
            "kind": "Deployment"
        },
        "resource": {
            "group": "apps",
            "version": "v1",
            "resource": "deployments"
        },
        "requestKind": {
            "group": "apps",
            "version": "v1",
            "kind": "Deployment"
        },
        "requestResource": {
            "group": "apps",
            "version": "v1",
            "resource": "deployments"
        },
        "name": "nginx",
        "operation": "CREATE",
        "userInfo": {
            "username": "kube-review",
            "uid": "611a19d7-6aa5-47d2-bba3-8c5df2bffbc7"
        },
        "object": {
            "kind": "Deployment",
            "apiVersion": "apps/v1",
            "metadata": {
                "name": "nginx",
                "creationTimestamp": null,
                "labels": {
                    "app": "nginx"
                }
            },
            "spec": {
                "selector": {
                    "matchLabels": {
                        "app": "nginx"
                    }
                },
                "template": {
                    "metadata": {
                        "creationTimestamp": null,
                        "labels": {
                            "app": "nginx"
                        }
                    },
                    "spec": {
                        "containers": [
                            {
                                "name": "nginx",
                                "image": "nginx",
                                "ports": [
                                    {
                                        "containerPort": 8080
                                    }
                                ],
                                "resources": {}
                            }
                        ]
                    }
                },
                "strategy": {}
            },
            "status": {}
        },
        "oldObject": null,
        "dryRun": true,
        "options": {
            "kind": "CreateOptions",
            "apiVersion": "meta.k8s.io/v1"
        }
    }
}

Why?

• Testing Kubernetes admission webhook receivers without Kubernetes (CI/CD pipelines, faster integration tests, etc.)
• Quickly be able to author, and test, admission control policies with tools like Open Policy Agent

Installation

Find the latest release for your platform at the release page. Once downloaded, rename it to kube-review (or kube-review.exe for Windows if not using WSL), allow it to be executed, and put it somewhere on your $PATH.

Running kube-review

kube-review create can either be provided a filename with a resource to create an admission review for, or can read data from stdin. This allows easily piping resources from a kube cluster and into kube-review.

Command

$ kubectl get service gatekeeper-webhook-service -o yaml | kube-review create --action update

Output

{
    "kind": "AdmissionReview",
    "apiVersion": "admission.k8s.io/v1",
    "request": {
        "uid": "b42420d7-5cc2-4644-992f-72ff67dc2889",
        "kind": {
            "group": "",
            "version": "v1",
            "kind": "Service"
        },
        "name": "gatekeeper-webhook-service",
        "namespace": "gatekeeper-system",
        "operation": "UPDATE",
        "userInfo": {
            "username": "kube-review",
            "uid": "42eac911-a8ec-4d72-9eb1-e6c466328085"
        },
        "...": "..."
    }
}

Command line options

Name	Type	Default	Description
--action	string	create	Type of operation to apply in admission review (create, update, delete, connect)
--as	string	kube-review	Name of user or service account for userInfo attributes
--as-group	string	none	Name of group this user or service account belongs to. May be repeated for multiple groups

The action provided has the following effects on the produced AdmissionReview object:

• create and connect: request.oldObject is null
• delete: request.object is null
• All actions change the value of request.operation and request.options

Using with Open Policy Agent

Assuming we have a policy that denies any deployment where the number of replicas is either undefined or below two:

package admission

deny["Deployment must have at least 2 replicas"] {
    input.request.object.spec.replicas < 2
}

deny["Deployment must define number of replicas explicitly"] {
    not input.request.object.spec.replicas
}

We could either run kube-review with a deployment from disk, and pipe the output into opa eval:

Command

$ kube-review create deployment.yaml \
| opa eval --format pretty --stdin-input --data policy.rego data.admission.deny

Output

[
  "Deployment must define number of replicas explicitly"
]

Or we could run the policy against any resource in our cluster in the same manner:

Command

$ kubectl get deployment my-microservice -o yaml \
| kube-review create \
| opa eval --format pretty --stdin-input --data policy.rego data.admission.deny

Output

[
  "Deployment must have at least 2 replicas"
]

Alternatively, we could use curl to send the data into a running OPA server:

Command

$ kubectl get deployment my-microservice -o yaml \
| kube-review create \
| curl --data-binary "@-" http://localhost:8181/v0/data/admission/deny

Output

[
    "Deployment must define number of replicas explicitly"
]

If your policies are written for OPA Gatekeeper, simply rename the request object in the admission request to review:

$ kube-review create deployment.yaml \
| opa eval --format pretty --stdin-input '{"review": input.request}' \
| opa eval --format pretty --stdin-input --data policy.rego data.admission.deny

Limitations

• kube-review can create AdmissionReview objects from CRDs, or any "Kubernetes-like" manifest, but it makes no attempt to verify that they conform to the schema of the corresponding CustomResourceDefinition.
• Currently, kube-review doesn't handle subresource requests.