Cluster Role

Usage and Concept of Cluster Role

The concept of cluster role is similar to role, but the difference is that cluster role is not namespaced. It is used to grant permissions to resources across all namespaces. Cluster roles are useful for cluster-wide permissions.

cluster-scoped resources (like nodes, namespaces, etc.)
non-resource endpoints (like /healthz, /version, etc.)
namespaced resources (like pods, services, etc.) across all namespaces
- For example, you can create a cluster role to grant access to all pods in all namespaces.

# list all resources under namespace
kubectl api-resources --namespaced=false
 
# this will help you to get the verb
kubectl api-resources --namespaced=false --sort-by name -o wide

NAME	APIVERSION	KIND
componentstatuses	v1	ComponentStatus
namespaces	v1	Namespace
nodes	v1	Node
persistentvolumes	v1	PersistentVolume
mutatingwebhookconfigurations	admissionregistration.k8s.io/v1	MutatingWebhookConfiguration
validatingadmissionpolicies	admissionregistration.k8s.io/v1	ValidatingAdmissionPolicy
validatingadmissionpolicybindings	admissionregistration.k8s.io/v1	ValidatingAdmissionPolicyBinding
validatingwebhookconfigurations	admissionregistration.k8s.io/v1	ValidatingWebhookConfiguration
customresourcedefinitions	apiextensions.k8s.io/v1	CustomResourceDefinition
apiservices	apiregistration.k8s.io/v1	APIService
selfsubjectreviews	authentication.k8s.io/v1	SelfSubjectReview
tokenreviews	authentication.k8s.io/v1	TokenReview
selfsubjectaccessreviews	authorization.k8s.io/v1	SelfSubjectAccessReview
selfsubjectrulesreviews	authorization.k8s.io/v1	SelfSubjectRulesReview
subjectaccessreviews	authorization.k8s.io/v1	SubjectAccessReview
certificatesigningrequests	certificates.k8s.io/v1	CertificateSigningRequest
flowschemas	flowcontrol.apiserver.k8s.io/v1	FlowSchema
prioritylevelconfigurations	flowcontrol.apiserver.k8s.io/v1	PriorityLevelConfiguration
ingressclasses	networking.k8s.io/v1	IngressClass
runtimeclasses	node.k8s.io/v1	RuntimeClass
clusterrolebindings	rbac.authorization.k8s.io/v1	ClusterRoleBinding
clusterroles	rbac.authorization.k8s.io/v1	ClusterRole
priorityclasses	scheduling.k8s.io/v1	PriorityClass
csidrivers	storage.k8s.io/v1	CSIDriver
csinodes	storage.k8s.io/v1	CSINode
storageclasses	storage.k8s.io/v1	StorageClass
volumeattachments	storage.k8s.io/v1	VolumeAttachment

Now, from the above table, we can see that clusterroles and clusterrolebindings are under cluster scope, meaning that they are created within a cluster. So, we no need to specify the namespace while creating them.

Step 1: Create a Cluster Role

You can use the following command to get the verb for the resource.

kubectl api-resources --namespaced=false --sort-by name -o wide

clusterrole.yaml

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: admin-reader
rules:
  - apiGroups: [""]
    resources: ["nodes"] # use * to allow all resources
    verbs: ["get", "list", "watch"]
  - apiGroups: [""]
    resources: ["secrets"] # accept namespaced resources as well
    verbs: ["get", "list", "watch"] # use * to allow all verbs
  - nonResourceURLs: ["/healthz", "/logs/*"]
    verbs: ["get"]

apiGroups - The API group of the resource. If you are not sure, you can see the above table (API Version).
resources: ["secrets"] - You can create a cluster role to grant access to all secrets in all namespaces. So, the user can access all secrets in all namespaces.

# You cannot create a role with different rules, as they will mix it up
kubectl create clusterrole admin-reader --verb=get,watch,list --resource=nodes
kubectl create clusterrole admin-reader --verb=get,watch,list --resource=secrets
kubectl create clusterrole admin-reader --verb=get --non-resource-url=/logs/*,/healthz
 
kubectl get clusterroles

Step 2: Create a Cluster Role Binding

Link the role to a user, group or service account.

rolebinding.yaml

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: admin-binding
subjects: # users, groups, or service accounts
  - kind: Group
    name: manager
    apiGroup: rbac.authorization.k8s.io
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: admin-reader # cluster role name

kubectl create clusterrolebinding admin-binding --role=admin-reader --group=manager
kubectl get clusterrolebinding

Usage and Concept of Cluster Role

Step 1: Create a Cluster Role

Step 2: Create a Cluster Role Binding

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