Comment on page
Kubernetes Role-Based Access Control(RBAC)
RBAC’s permission model is built from three individual parts:
- 2.Subject (User, Group or ServiceAccount) – The object that will receive the permissions.
- 3.RoleBinding\ClusterRoleBinding – The connection between Role\ClusterRole and the subject.
The difference between “Roles” and “ClusterRoles” is just where the role will be applied – a “Role” will grant access to only one specific namespace, while a “ClusterRole” can be used in all namespaces in the cluster. Moreover, ClusterRoles can also grant access to:
- cluster-scoped resources (like nodes).
- non-resource endpoints (like /healthz).
- namespaced resources (like Pods), across all namespaces.
From Kubernetes 1.6 onwards, RBAC policies are enabled by default. But to enable RBAC you can use something like:
kube-apiserver --authorization-mode=Example,RBAC --other-options --more-options
In the template of a Role or a ClusterRole you will need to indicate the name of the role, the namespace (in roles) and then the apiGroups, resources and verbs of the role:
- The apiGroups is an array that contains the different API namespaces that this rule applies to. For example, a Pod definition uses apiVersion: v1. It can has values such as rbac.authorization.k8s.io or [*].
- The resources is an array that defines which resources this rule applies to. You can find all the resources with:
kubectl api-resources --namespaced=true
- The verbs is an array that contains the allowed verbs. The verb in Kubernetes defines the type of action you need to apply to the resource. For example, the list verb is used against collections while "get" is used against a single resource.
Kubernetes sometimes checks authorization for additional permissions using specialized verbs. For example:
You can find all the verbs that each resource support executing
kubectl api-resources --sort-by name -o wide
- apiGroups: [""]
resources: ["pods", "pods/log"]
verbs: ["get", "list", "watch"]
# "namespace" omitted since ClusterRoles are not namespaced
- apiGroups: [""]
verbs: ["get", "watch", "list"]
For example you can use a ClusterRole to allow a particular user to run:
kubectl get pods --all-namespaces
A role binding grants the permissions defined in a role to a user or set of users. It holds a list of subjects (users, groups, or service accounts), and a reference to the role being granted. A RoleBinding grants permissions within a specific namespace whereas a ClusterRoleBinding grants that access cluster-wide.
# This role binding allows "jane" to read pods in the "default" namespace.
# You need to already have a Role named "pod-reader" in that namespace.
# You can specify more than one "subject"
- kind: User
name: jane # "name" is case sensitive
# "roleRef" specifies the binding to a Role / ClusterRole
kind: Role #this must be Role or ClusterRole
name: pod-reader # this must match the name of the Role or ClusterRole you wish to bind to
# This cluster role binding allows anyone in the "manager" group to read secrets in any namespace.
- kind: Group
name: manager # Name is case sensitive
Permissions are additive so if you have a clusterRole with “list” and “delete” secrets you can add it with a Role with “get”. So be aware and test always your roles and permissions and specify what is ALLOWED, because everything is DENIED by default.
# Get current privileges
kubectl auth can-i --list
# use `--as=system:serviceaccount:<namespace>:<sa_name>` to impersonate a service account
# List Cluster Roles
kubectl get clusterroles
kubectl describe clusterroles
# List Cluster Roles Bindings
kubectl get clusterrolebindings
kubectl describe clusterrolebindings
# List Roles
kubectl get roles
kubectl describe roles
# List Roles Bindings
kubectl get rolebindings
kubectl describe rolebindings