Role-Based Access Control (RBAC)

Role-based access control (RBAC) is a method of regulating access to computer or network resources based on the roles of individual users within your organization.

RBAC authorization uses the rbac.authorization.k8s.io API group to drive authorization decisions, allowing you to dynamically configure policies through the Kubernetes API.

Role and Cluster Role

An RBAC Role or ClusterRole contains rules that represent a set of permissions. Permissions are purely additive (there are no "deny" rules).

A Role always sets permissions within a particular namespace; when you create a Role, you have to specify the namespace it belongs in.

ClusterRole, by contrast, is a non-namespaced resource. The resources have different names (Role and ClusterRole) because a Kubernetes object always has to be either namespaced or not namespaced; it can't be both.

RoleBinding and ClusterRoleBinding

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.

A RoleBinding may reference any Role in the same namespace. Alternatively, a RoleBinding can reference a ClusterRole and bind that ClusterRole to the namespace of the RoleBinding. If you want to bind a ClusterRole to all the namespaces in your cluster, you use a ClusterRoleBinding.

Example

• Let's try create new cluster role pod-reader in role.yaml file.

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: pod-reader
rules:
- apiGroups: [""] # "" indicates the core API group
  resources: ["pods"]
  verbs: ["get", "watch", "list"]

• Apply the configuration using kubectl apply -f role.yaml.

• Check the cluster roles using kubectl get clusterrole. The cluster role pod-reader should be in the list.

• Now lets try to bind this role to a user.

• Add below configuration into our role.yaml file.

---
apiVersion: rbac.authorization.k8s.io/v1
# 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.
kind: ClusterRoleBinding
metadata:
  name: read-pods
subjects:
# You can specify more than one "subject"
- kind: User
  name: jane # "name" is case sensitive
  apiGroup: rbac.authorization.k8s.io
roleRef:
  # "roleRef" specifies the binding to a Role / ClusterRole
  kind: ClusterRole #this must be Role or ClusterRole
  name: pod-reader # this must match the name of the Role or ClusterRole you wish to bind to
  apiGroup: rbac.authorization.k8s.io

• This configuration will bind cluster role pod-reader into user jane.

• Apply the configuration kubectl apply -f role.yaml.

• Try it using below commands

kubectl --as=jane get pods
kubectl --as=jane get nodes

• The first command should return list of pods

• The second command should return and error below:

Error from server (Forbidden): nodes is forbidden: User "jane" cannot list resource "nodes" in API group "" at the cluster scope