RBACs in kubernetes

The kubernetes provides a Role based Access controls as a immediate mechanism as a security measure.

The roles are the grouping of PolicyRules and the capabilities and limitations within a namespace.
The Identities (or) Subjects are the users/ServiceAccounts which are assigned Roles which constitute a RBACs.
This process is acheived by referencing a role from RoleBinding to create RBACs.

In kubernetes there is Role and RoleBindings and the ClusterRole and ClusterRoleBinding.

There is no concept of a deny permission in the RBACs.

The Role and the Subject combined together defines a RoleBinding.

Now lets look at each of the terms in detail.

Subjects:

  • user
  • group
  • serviceAccount

Resources:

  • configmaps
  • pods
  • services

Verbs:

  • create
  • delete
  • get
  • list
  • patch
  • proxy
  • update
  • watch

You Create a kind:Role with a name and then binding with roleRef it to Subject by creating a kind: RoleBinding

[vamshi@master01 k8s]$ kubectl describe serviceaccounts builduser01 
Name:                builduser01
Namespace:           default
Labels:              
Annotations:         
Image pull secrets:  
Mountable secrets:   builduser01-token-rmjsd
Tokens:              builduser01-token-rmjsd
Events:              

The role builduser-role has the permissions to all the resources to create, delete, get, list, patch, update and watch.

[vamshi@master01 k8s]$ kubectl describe role builduser-role
Name: builduser-role
Labels:
Annotations: kubectl.kubernetes.io/last-applied-configuration:
{"apiVersion":"rbac.authorization.k8s.io/v1","kind":"Role","metadata":{"annotations":{},"name":"builduser-role","namespace":"default"},"ru...
PolicyRule:
Resources Non-Resource URLs Resource Names Verbs
--------- ----------------- -------------- -----
* [] [] [create delete get list patch update watch]

Using this you can limit the user access to your cluster

View the current clusterbindings on your kubernetes custer

[vamshi@master01 :~] kubectl get clusterrolebinding
NAME                                                   AGE
cluster-admin                                          2d2h
kubeadm:kubelet-bootstrap                              2d2h
kubeadm:node-autoapprove-bootstrap                     2d2h
kubeadm:node-autoapprove-certificate-rotation          2d2h
kubeadm:node-proxier                                   2d2h
minikube-rbac                                          2d2h
storage-provisioner                                    2d2h
system:basic-user                                      2d2h

The clusterrole describes the Resources and the verbs that are accessible the user.

[vamshi@linux-r5z3:~] kubectl describe clusterrole cluster-admin
Name:         cluster-admin
Labels:       kubernetes.io/bootstrapping=rbac-defaults
Annotations:  rbac.authorization.kubernetes.io/autoupdate: true
PolicyRule:
  Resources  Non-Resource URLs  Resource Names  Verbs
  ---------  -----------------  --------------  -----
  *.*        []                 []              [*]
             [*]                []              [*]

Listing the roles on Kubernetes:

[vamshi@master01 :~] kubectl get roles --all-namespaces
NAMESPACE     NAME                                             AGE
kube-public   kubeadm:bootstrap-signer-clusterinfo             2d2h
kube-public   system:controller:bootstrap-signer               2d2h
kube-system   extension-apiserver-authentication-reader        2d2h
kube-system   kube-proxy                                       2d2h
kube-system   kubeadm:kubelet-config-1.15                      2d2h
kube-system   kubeadm:nodes-kubeadm-config                     2d2h
kube-system   system::leader-locking-kube-controller-manager   2d2h
kube-system   system::leader-locking-kube-scheduler            2d2h
kube-system   system:controller:bootstrap-signer               2d2h
kube-system   system:controller:cloud-provider                 2d2h
kube-system   system:controller:token-cleaner                  2d2h

We can further examine the rolebindings on the for the name: system::leader-locking-kube-scheduler which is being associated with the service account kube-scheduler.

[vamshi@master01 :~]  kubectl describe rolebindings system::leader-locking-kube-scheduler -n kube-system
Name:         system::leader-locking-kube-scheduler
Labels:       kubernetes.io/bootstrapping=rbac-defaults
Annotations:  rbac.authorization.kubernetes.io/autoupdate: true
Role:
  Kind:  Role
  Name:  system::leader-locking-kube-scheduler
Subjects:
  Kind            Name                   Namespace
  ----            ----                   ---------
  User            system:kube-scheduler  
  ServiceAccount  kube-scheduler         kube-system

There is a category of the api groups which contains the following api tags:

apiextensions.k8s.io, apps, autoscaling, batch, Binding, certificates.k8s.io, events.k8s.io, extensions, networking.k8s.io, PodTemplate, policy, scheduling.k8s.io, Secret, storage.k8s.io

The complete roles available in Kubernetes are as follows:

APIService, CertificateSigningRequest, ClusterRole, ClusterRoleBinding, ComponentStatus, ConfigMap, ControllerRevision, CronJob, CSIDriver, CSINode, CustomResourceDefinition, DaemonSet, Deployment, Endpoints, Event, HorizontalPodAutoscaler, Ingress, Job, Lease, LimitRange, LocalSubjectAccessReview, MutatingWebhookConfiguration, Namespace, NetworkPolicy, Node, PersistentVolume, PersistentVolumeClaim, Pod, PodDisruptionBudget, PodSecurityPolicy, PriorityClass, ReplicaSet, ReplicationController, ResourceQuota, Role, RoleBinding, RuntimeClass, SelfSubjectAccessReview, SelfSubjectRulesReview, Service, ServiceAccount, StatefulSet, StorageClass, SubjectAccessReview, TokenReview, ValidatingWebhookConfiguration and VolumeAttachment

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