Solution Cluster Roles

In this lesson, we will explore the concepts of cluster roles and cluster role bindings. We will inspect the existing cluster roles and their bindings, count them, and review their permissions before creating new roles and bindings for a new team member named Michelle.

Inspecting Existing Cluster Roles

Begin by examining the currently defined cluster roles in your cluster. These roles include cluster-admin, system-specific roles, and others. Run the following command to list them:

system:volume-scheduler
system:certificates.k8s.io:legacy-unknown-approver
system:certificates.k8s.io:kubelet-serving-approver
system:certificates.k8s.io:kube-apiserver-client-approver
system:certificates.k8s.io:kube-apiserver-client-kubelet-approver
system:service-account-issuer-discovery
system:node-proxier
system:kube-scheduler
system:controller:attacheddetach-controller
system:controller:clusteroverlay-aggregation-controller
system:controller:cronjob-controller
system:controller:daemon-set-controller
system:controller:deployment-controller
system:controller:endpoint-controller
system:controller:endpointslice-mirroring-controller
system:controller:expand-controller
system:controller:ephemeral-volume-controller
system:controller:generic-garbage-collector
system:controller:job-controller
system:controller:namespace-controller
system:controller:node-controller
system:controller:persistent-volume-binder
system:controller:garbage-collector
system:controller:replicaset-controller
system:controller:replication-controller
system:controller:resourcequota-controller
system:controller:service-account-controller
system:controller:service-controller
system:controller:statefulset-controller
system:controller:ttl-controller
system:controller:vertical-pod-autoscaler
system:controller:volume-protection-controller
system:controller:ttl-after-finished-controller
system:controller:root-ca-cert-publisher
k3s-cloud-controller-manager

You can count these roles manually by piping the output to wc -l. For example:

k get clusterroles --no-headers | wc -l

On one system, this command produced an output of 6, but keep in mind that this example shows a truncated list. In another instance, a total of 69 roles might be expected using a different counting method.

Inspecting Cluster Role Bindings

Next, verify the cluster role bindings by counting them with the following command:

k get clusterrolebindings --no-headers | wc -l

This command returned 54 on the system in question, indicating that there are 54 cluster role bindings.

To illustrate further, here is an excerpt displaying some cluster roles and their creation times:

k get clusterroles
NAME                                                                  CREATED AT
cluster-admin                                                       2022-04-18T00:01:23Z
system:discovery                                                   2022-04-18T00:01:23Z
system:monitoring                                                  2022-04-18T00:01:23Z
system:basic-user                                                  2022-04-18T00:01:23Z
system:public-info-viewer                                          2022-04-18T00:01:23Z
system:aggregate-to-admin                                          2022-04-18T00:01:23Z
system:aggregate-to-edit                                           2022-04-18T00:01:23Z
system:aggregate-to-view                                           2022-04-18T00:01:23Z
system:heapster                                                    2022-04-18T00:01:23Z
system:node                                                       2022-04-18T00:01:23Z
...

Reviewing Cluster Admin Role Bindings

The cluster-admin role represents the highest permission level and is bound to specific user groups via a ClusterRoleBinding. To identify the binding for the cluster-admin role, run:

k get clusterrolebindings | grep cluster-admin

The output may appear as follows:

cluster-admin                    12m   ClusterRole/cluster-admin
helm-kube-system-traefik         12m   ClusterRole/cluster-admin
helm-kube-system-traefik-crd     12m   ClusterRole/cluster-admin

You can then inspect the details of the cluster-admin binding with:

k describe clusterrolebindings cluster-admin

This command produces output similar to:

Name:         cluster-admin
Labels:       kubernetes.io/bootstraping=rbac-defaults
Annotations:  rbac.authorization.kubernetes.io/autoupdate: true
Role:
  Kind:  ClusterRole
  Name:  cluster-admin
Subjects:
  Kind  Name                 Namespace
  ----- ------------------- -----------
  Group system:masters

This confirms that the cluster-admin role is bound by default to the system:masters group, thereby granting all possible operations (denoted by [*] for all actions on all resources).

Granting Node Access to a New User (Michelle)

Michelle, a new team member, requires access to manage nodes. Initially, when Michelle runs:

k get nodes --as michelle

she encounters the following error:

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

To resolve this issue, follow these steps:

Create the Cluster Role for Node Access

Create a cluster role named michelle-role that allows Michelle to get, list, and watch nodes:

k create clusterrole michelle-role --verb=get,list,watch --resource=nodes

Verify the new role by describing it:

k describe clusterrole michelle-role

Expected output:

Name:         michelle-role
Labels:       <none>
Annotations:  <none>
PolicyRule:
  Resources   Non-Resource URLs   Resource Names   Verbs
  ---------   -----------------   ---------------  ---------
  nodes       []                  []               [get list watch]

Bind the Cluster Role to Michelle

Bind the role to Michelle’s user account with:

k create clusterrolebinding michelle-role-binding --clusterrole=michelle-role --user=michelle

Verify this binding with:

k describe clusterrolebinding michelle-role-binding

Expected output:

Name:         michelle-role-binding
Labels:       <none>
Annotations:  <none>
Role:
  Kind:  ClusterRole
  Name:  michelle-role
Subjects:
  Kind   Name      Namespace
  ----   ----      ---------
  User   michelle

Finally, test Michelle’s access again:

k get nodes --as michelle

A successful command execution will display a list of nodes similar to:

NAME         STATUS   ROLES                 AGE   VERSION
controlplane Ready    control-plane,master  16m   v1.23.3+k3s1

Expanding Michelle's Responsibilities to Storage

Michelle’s roles are expanding to include storage management. To grant her access to storage-related resources, first verify the available API resources by running:

kubectl api-resources

This command lists resources along with their short names, API versions, and scope. For storage management, the key resources are persistent volumes and storage classes.

Create a Cluster Role for Storage Administration

Create a cluster role named storage-admin that allows listing, creating, getting, and watching persistent volumes and storage classes:

k create clusterrole storage-admin --resource=persistentvolumes,storageclasses --verb=list,create,get,watch

Verify the role in YAML format using:

k get clusterrole storage-admin -o yaml

An expected YAML output is as follows:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  creationTimestamp: "2022-04-18T00:20:48Z"
  name: storage-admin
  resourceVersion: "921"
  uid: e0ee52a7-b32c-4a42-bb7a-a783b040cd4e
rules:
- apiGroups:
  - ""
  resources:
  - persistentvolumes
  verbs:
  - list
  - create
  - get
  - watch
- apiGroups:
  - storage.k8s.io
  resources:
  - storageclasses
  verbs:
  - list
  - create
  - get
  - watch

Bind the Storage Admin Role to Michelle

Bind the storage-admin role to Michelle with the following command:

k create clusterrolebinding michelle-storage-admin --user=michelle --clusterrole=storage-admin

Verify this binding:

k describe clusterrolebinding michelle-storage-admin

Expected output:

Name:         michelle-storage-admin
Labels:       <none>
Annotations:  <none>
Role:
  Kind:  ClusterRole
  Name:  storage-admin
Subjects:
  Kind   Name      Namespace
  ----   ----      ---------
  User   michelle

Michelle should now have the necessary permissions to manage storage resources such as persistent volumes and storage classes.

This concludes the lesson on inspecting, creating, and binding cluster roles and cluster role bindings. By following these steps, you learned how to review existing roles, grant specific permissions to a user, and expand those permissions as job responsibilities change.