non-resource-url

non-resource-url example

Note to try this out with minikube, make sure you enable RBAC correctly as explained here.

RBAC differentiates in two types, that need to be authorized, resources and non-resources. A resource request authorization, could for example be, that a requesting entity needs to be authorized to perform the get action on a particular Kubernetes Deployment. A non-resource authorization validates, that an entity is authorized to request a bare URL.

Take the following example. We want to deploy a prometheus-example-app, and protect its /metrics endpoint. This endpoint does not correspond to a resource, and is therefore treated as a non-resource-url in RBAC. For non-resource-url authorizations there are no extra arguments required to be passed to the kube-rbac-proxy besides the --upstream flag in order for it to perform the authorization.

The kube-rbac-proxy itself also requires RBAC access, in order to perform TokenReviews as well as SubjectAccessReviews. These are the APIs available from the Kubernetes API to authenticate and then validate the authorization of an entity.

$ kubectl create -f deployment.yaml

The content of this manifest is:

apiVersion: v1
kind: ServiceAccount
metadata:
  name: kube-rbac-proxy
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: kube-rbac-proxy
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: kube-rbac-proxy
subjects:
- kind: ServiceAccount
  name: kube-rbac-proxy
  namespace: default
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: kube-rbac-proxy
rules:
- apiGroups: ["authentication.k8s.io"]
  resources:
  - tokenreviews
  verbs: ["create"]
- apiGroups: ["authorization.k8s.io"]
  resources:
  - subjectaccessreviews
  verbs: ["create"]
---
apiVersion: v1
kind: Service
metadata:
  labels:
    app: kube-rbac-proxy
  name: kube-rbac-proxy
spec:
  ports:
  - name: https
    port: 8443
    targetPort: https
  selector:
    app: kube-rbac-proxy
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: kube-rbac-proxy
spec:
  replicas: 1
  selector:
    matchLabels:
      app: kube-rbac-proxy
  template:
    metadata:
      labels:
        app: kube-rbac-proxy
    spec:
      securityContext:
        runAsUser: 65532
      serviceAccountName: kube-rbac-proxy
      containers:
      - name: kube-rbac-proxy
        image: quay.io/brancz/kube-rbac-proxy:v0.18.1
        args:
        - "--secure-listen-address=0.0.0.0:8443"
        - "--upstream=http://127.0.0.1:8081/"
        - "--logtostderr=true"
        - "--v=10"
        ports:
        - containerPort: 8443
          name: https
        securityContext:
          allowPrivilegeEscalation: false
      - name: prometheus-example-app
        image: quay.io/brancz/prometheus-example-app:v0.5.0
        args:
        - "--bind=127.0.0.1:8081"

Once the prometheus-example-app is up and running, we can test it. In order to test it, we deploy a Job, that performs a curl against the above deployment. Because it has the /metrics path in its nonResourceURLs it is allowed to access the endpoint.

The Dockerfile of this container can be found here.

$ kubectl create -f client-rbac.yaml client.yaml

The content of this manifest is:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: metrics
rules:
- nonResourceURLs: ["/metrics"]
  verbs: ["get"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: metrics
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: metrics
subjects:
- kind: ServiceAccount
  name: default
  namespace: default

apiVersion: batch/v1
kind: Job
metadata:
  name: krp-curl
spec:
  template:
    metadata:
      name: krp-curl
    spec:
      containers:
      - name: krp-curl
        image: quay.io/brancz/krp-curl:v0.0.2
      restartPolicy: Never
  backoffLimit: 4

We can look at the logs and we should get something similar to:

$ kubectl logs job/krp-curl
*   Trying 10.99.141.73...
* TCP_NODELAY set
* Connected to kube-rbac-proxy.default.svc (10.99.141.73) port 8080 (#0)
> GET /metrics HTTP/1.1
> Host: kube-rbac-proxy.default.svc:8080
> User-Agent: curl/7.57.0
> Accept: */*
> Authorization: Bearer eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJrdWJlcm5ldGVzL3NlcnZpY2VhY2NvdW50Iiwia3ViZXJuZXRlcy5pby9zZXJ2aWNlYWNjb3VudC9uYW1lc3BhY2UiOiJkZWZhdWx0Iiwia3ViZXJuZXRlcy5pby9zZXJ2aWNlYWNjb3VudC9zZWNyZXQubmFtZSI6ImRlZmF1bHQtdG9rZW4tNHBzeHYiLCJrdWJlcm5ldGVzLmlvL3NlcnZpY2VhY2NvdW50L3NlcnZpY2UtYWNjb3VudC5uYW1lIjoiZGVmYXVsdCIsImt1YmVybmV0ZXMuaW8vc2VydmljZWFjY291bnQvc2VydmljZS1hY2NvdW50LnVpZCI6IjY2YTAzNTdiLWUzMmYtMTFlNy04YjIzLTA4MDAyNzhkNDA5OSIsInN1YiI6InN5c3RlbTpzZXJ2aWNlYWNjb3VudDpkZWZhdWx0OmRlZmF1bHQifQ.egkmiNUcs8gB9I1EHPwdzr-xYjVK5dpd8OihPkMiM1DjRN7PoVVTWiM9IWBo2gZRGxV8ItpwCFDALs2Y85nfZk8l82YE6qHdQHG3-igqbiNNwRUIkVcpNpKmA-859LdC3C2ia0cnvll_ge1FlVOWMGH8rvSwD4-We2xbEwJ6djmBMF3iN6zHmeiom8WGKxoF3ddKoCKhLEN9pTiOVeXitWm6U2xEj_WyrMSpaIlfoT-BxNSOxTTPo5Nk71yM1bEzGb6jQdixOPsgHZP0nNxf9tmWnyb9qjBOPzObze9GHAoJUx9a94rURR8Zpf6DgPtKMJxcNq2buI05RdBwCkfjug
>
< HTTP/1.1 200 OK
< Content-Type: text/plain; version=0.0.4
< Date: Sun, 17 Dec 2017 13:40:00 GMT
< Content-Length: 102
<
{ [102 bytes data]
* Connection #0 to host kube-rbac-proxy.default.svc left intact
# HELP version Version information about this binary
# TYPE version gauge
version{version="v0.1.0"} 0