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Role-based access control for the Prometheus operator

Role-based access control (RBAC) for the Prometheus Operator involves two parts, RBAC rules for the Operator itself and RBAC rules for the Prometheus Pods themselves created by the Operator as Prometheus requires access to the Kubernetes API for target and Alertmanager discovery.

Prometheus Operator RBAC

In order for the Prometheus Operator to work in an RBAC based authorization environment, a ClusterRole with access to all the resources the Operator requires for the Kubernetes API needs to be created. This section is intended to describe, why the specified rules are required.

Here is a ready to use manifest of a ClusterRole that can be used to start the Prometheus Operator:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  labels:
    app.kubernetes.io/component: controller
    app.kubernetes.io/name: prometheus-operator
    app.kubernetes.io/version: 0.58.0
  name: prometheus-operator
rules:
- apiGroups:
  - monitoring.coreos.com
  resources:
  - alertmanagers
  - alertmanagers/finalizers
  - alertmanagerconfigs
  - prometheuses
  - prometheuses/finalizers
  - prometheuses/status
  - thanosrulers
  - thanosrulers/finalizers
  - servicemonitors
  - podmonitors
  - probes
  - prometheusrules
  verbs:
  - '*'
- apiGroups:
  - apps
  resources:
  - statefulsets
  verbs:
  - '*'
- apiGroups:
  - ""
  resources:
  - configmaps
  - secrets
  verbs:
  - '*'
- apiGroups:
  - ""
  resources:
  - pods
  verbs:
  - list
  - delete
- apiGroups:
  - ""
  resources:
  - services
  - services/finalizers
  - endpoints
  verbs:
  - get
  - create
  - update
  - delete
- apiGroups:
  - ""
  resources:
  - nodes
  verbs:
  - list
  - watch
- apiGroups:
  - ""
  resources:
  - namespaces
  verbs:
  - get
  - list
  - watch
- apiGroups:
  - networking.k8s.io
  resources:
  - ingresses
  verbs:
  - get
  - list
  - watch

Note: A cluster admin is required to create this ClusterRole and create a ClusterRoleBinding or RoleBinding to the ServiceAccount used by the Prometheus Operator Pod. The ServiceAccount used by the Prometheus Operator Pod can be specified in the Deployment object used to deploy it.

As the Prometheus Operator works extensively with its customresourcedefinitions, it requires all actions on those objects. Those are:

  • alertmanagers
  • podmonitors
  • probes
  • prometheuses
  • prometheusrules
  • servicemonitors
  • thanosrulers

Alertmanager and Prometheus clusters are created using statefulsets therefore all changes to an Alertmanager or Prometheus object result in a change to the statefulsets, which means all actions must be permitted.

Additionally as the Prometheus Operator generates configurations, it requires all actions on configmaps and secrets.

When the Prometheus Operator performs version migrations from one version of Prometheus or Alertmanager to the other, it needs to list pods running an old version and delete those.

The Prometheus Operator reconciles services called prometheus-operated and alertmanager-operated, which are used as governing Services for the StatefulSets. To perform this reconciliation it needs the permission to get, create, update and delete these services.

As the kubelet is currently not self-hosted, the Prometheus Operator has a feature to synchronize the IPs of the kubelets into an Endpoints object, which requires access to list and watch of nodes (kubelets) and create and update for the endpoints resource.

Prometheus RBAC

The Prometheus server itself accesses the Kubernetes API to discover targets and Alertmanagers. Therefore a separate ClusterRole for those Prometheus servers needs to exist.

As Prometheus does not modify any Objects in the Kubernetes API, but just reads them it simply requires the get, list, and watch actions. As Prometheus can also be used to scrape metrics from the Kubernetes apiserver, it also requires access to the /metrics/ endpoint of it.

In addition to the rules for Prometheus itself, the Prometheus sidecar needs to be able to get configmaps to be able to pull in rule files from configmap objects.

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: prometheus
rules:
- apiGroups: [""]
  resources:
  - nodes
  - nodes/metrics
  - services
  - endpoints
  - pods
  verbs: ["get", "list", "watch"]
- apiGroups: [""]
  resources:
  - configmaps
  verbs: ["get"]
- apiGroups:
  - networking.k8s.io
  resources:
  - ingresses
  verbs: ["get", "list", "watch"]
- nonResourceURLs: ["/metrics"]
  verbs: ["get"]

Note: A cluster admin is required to create this ClusterRole and create a ClusterRoleBinding or RoleBinding to the ServiceAccount used by the Prometheus Pods. The ServiceAccount used by the Prometheus Pods can be specified in the Prometheus object.

Example

To demonstrate how to use a ClusterRole with a ClusterRoleBinding and a ServiceAccount here an example. It is assumed, that both of the ClusterRoles described above have already been created.

Say the Prometheus Operator shall be deployed in the default namespace. First a ServiceAccount needs to be setup.

apiVersion: v1
automountServiceAccountToken: false
kind: ServiceAccount
metadata:
  labels:
    app.kubernetes.io/component: controller
    app.kubernetes.io/name: prometheus-operator
    app.kubernetes.io/version: 0.58.0
  name: prometheus-operator
  namespace: default

Note that the ServiceAccountName also has to actually be used in spec.template.spec.serviceAccount of the Deployment of the Prometheus Operator.

And then a ClusterRoleBinding:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  labels:
    app.kubernetes.io/component: controller
    app.kubernetes.io/name: prometheus-operator
    app.kubernetes.io/version: 0.58.0
  name: prometheus-operator
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: prometheus-operator
subjects:
- kind: ServiceAccount
  name: prometheus-operator
  namespace: default

Because the Pod that the Prometheus Operator is running in uses the ServiceAccount named prometheus-operator and the ClusterRoleBinding associates it with the ClusterRole named prometheus-operator, it now has the required permissions to access all the resources as described above.

When creating Prometheus objects the procedure is similar. It starts with a ServiceAccount.

apiVersion: v1
kind: ServiceAccount
metadata:
  name: prometheus

And then because the ClusterRole named prometheus, as described above, is likely to be used multiple times, a ClusterRoleBinding instead of a RoleBinding is used.

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: prometheus
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: prometheus
subjects:
- kind: ServiceAccount
  name: prometheus
  namespace: default

See Using Authorization Plugins for further usage information on RBAC components.