Role-based access control

This page provides an overview for the role-based access control (RBAC) system provided by Kubernetes, and how you can use Kubernetes RBAC in Google Kubernetes Engine (GKE).

Overview

Kubernetes includes a built-in role-based access control (RBAC) mechanism that enables you to configure fine-grained and specific sets of permissions that define how a given Google Cloud user, or group of users, can interact with any Kubernetes object in your cluster, or in a specific Namespace of your cluster.

Kubernetes RBAC is enabled by default.

Before you begin

Before you start, make sure you have performed the following tasks:

Set up default gcloud settings using one of the following methods:

  • Using gcloud init, if you want to be walked through setting defaults.
  • Using gcloud config, to individually set your project ID, zone, and region.

Using gcloud init

  1. Run gcloud init and follow the directions:

    gcloud init

    If you are using SSH on a remote server, use the --console-only flag to prevent the command from launching a browser:

    gcloud init --console-only
  2. Follow the instructions to authorize gcloud to use your Google Cloud account.
  3. Create a new configuration or select an existing one.
  4. Choose a Google Cloud project.
  5. Choose a default Compute Engine zone.

Using gcloud config

  • Set your default project ID:
    gcloud config set project project-id
  • If you are working with zonal clusters, set your default compute zone:
    gcloud config set compute/zone compute-zone
  • If you are working with regional clusters, set your default compute region:
    gcloud config set compute/region compute-region
  • Update gcloud to the latest version:
    gcloud components update

Interaction with Identity and Access Management

You can use both Cloud Identity and Access Management and Kubernetes RBAC to control access to your GKE cluster:

  • Cloud IAM is not specific to Kubernetes; it provides identity management for multiple Google Cloud products, and operates primarily at the level of the Google Cloud project.

  • Kubernetes RBAC is a core component of Kubernetes and lets you create and grant roles (sets of permissions) for any object or type of object within the cluster.

In GKE, Cloud IAM and Kubernetes RBAC are integrated to authorize users to perform actions if they have sufficient permissions according to either tool. This is an important part of bootstrapping a GKE cluster, since by default Google Cloud users do not have any Kubernetes RBAC RoleBindings.

To authorize users using Google Cloud accounts, the client must be correctly configured to authenticate using those accounts first. For example, if you are using kubectl, you must configure the kubectl command to authenticate to Google Cloud before running any commands that require authorization.

While Kubernetes RBAC can be used instead of Cloud IAM for almost all cases, GKE users are required at least the container.clusters.get Cloud IAM permission in the project containing the cluster. This permission is included by the container.clusterViewer role, as well as the other, more highly privileged roles. The container.clusters.get permission is required for users to authenticate to the clusters in the project, but does not authorize them to perform any actions inside those clusters. Authorization may then be provided by either Cloud IAM or Kubernetes RBAC.

Prerequisites for using Kubernetes RBAC on GKE cluster v1.11.x and older

In GKE clusters using GKE v1.11.x and older, there is a limitation that Cloud IAM cannot grant the ability to create a Kubernetes RBAC Role or ClusterRole. However, the Kubernetes Engine Admin Cloud IAM role does grant users with the ability to create a Kubernetes RBAC RoleBinding or ClusterRoleBinding for any user, including themselves, which can be used to bind Google Cloud users to predefined RBAC Roles.

In particular, the cluster-admin predefined RBAC role grants users full permissions in the cluster. Therefore, to bootstrap a user to allow them to create RBAC Roles and ClusterRoles, issue the following command, replacing user-account with the target user's Google Cloud login email address.

kubectl create clusterrolebinding cluster-admin-binding \
  --clusterrole cluster-admin \
  --user user-account

Google Groups for GKE

Previously, you could only grant roles to Google Cloud user accounts or Cloud IAM service accounts. Google Groups for GKE (Beta) enables you to grant roles to the members of a G Suite Google Group. With this mechanism, the users and groups themselves are maintained by your G Suite administrators, completely outside of Kubernetes or Cloud Console, so your cluster administrators do not need detailed information about your users. Another benefit is integration with your existing user account management practices, such as revoking access when someone leaves your organization.

To use this feature, complete the following tasks:

Requirements

Using Google Groups for GKE has the following requirements:

  • You must have a G Suite or Cloud Identity subscription.

Configure Google Groups for use with RBAC

Configuring your cluster to use this feature, as well as the syntax for referencing a G Suite Google Group in Kubernetes RBAC is discussed later in this topic. First, you need to set up your Google Groups following the steps below:

  1. Create a G Suite Google Group in your domain, named gke-security-groups@yourdomain.com. The group must be named exactly gke-security-groups. Make sure the gke-security-groups group has the "View Members" permission for "Group Members". See this article for an example of how to set this in the G Suite Admin Console.

    You may also refer to the Groups Help Center for more information on managing Groups in G Suite.

  2. Create groups, if they do not already exist, that represent groups of users or groups who should have different permissions on your clusters. Each group must have the "View Members" permission for "Group Members".

  3. Add these groups (not users) to the membership of gke-security-groups@yourdomain.com.

To check whether a given user has permission to create, modify, or view a resource in the cluster based on group membership, GKE checks both whether the user is a member of a group with access, and whether that group is a direct member of your domain's gke-security-groups group. The user must also belong to the same domain as the group and the cluster. This means cross domain authorization does not work with this feature.

Information about G Suite Google Group membership is cached for a short time. It may take a few minutes for changes in group memberships to propagate to all of your clusters. In addition to latency from groups changes, standard caching of user credentials on the cluster is about one hour.

Configuring your cluster to use Google Groups for GKE

After your G Suite Google Groups administrator sets up your groups, create a new cluster using the gcloud command, and add the --security-group="gke-security-groups@yourdomain.com" flag, substituting the value with your own domain name.

The following is an example of the cluster create command:

gcloud beta container clusters create cluster-name \
  --security-group="gke-security-groups@yourdomain.com"

Now you are ready to create Roles, ClusterRoles, RoleBindings, and ClusterRoleBindings that reference your G Suite Google Groups.

Defining and assigning permissions

You define your RBAC permissions by creating the following kinds of Kubernetes objects:

  • ClusterRole or Role: defines a set of resource types and operations that can be assigned to a user or group of users in a cluster (ClusterRole), or a Namespace (Role), but does not specify the user or group of users.
  • ClusterRoleBinding or RoleBinding: assigns a ClusterRole or Role to a user or group of users. A ClusterRoleBinding works with a ClusterRole, and a RoleBinding works with either a ClusterRole or a Role.

RBAC roles are purely additive--there are no "deny" rules. When structuring your RBAC roles, you should think in terms of "granting" users access to cluster resources.

Defining Permissions using Roles or ClusterRoles

You define permissions within a Role or ClusterRole object. A Role defines access to resources within a single Namespace, while a ClusterRole defines access to resources in the entire cluster.

Roles and ClusterRoles have the same syntax. Each has a rules section, where you define the relevant Namespace, resource type, and allowable operations for the Role. For example, the following Role grants read access (get, watch, and list) for all Pods in the accounting Namespace:

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

Role vs. ClusterRole

Because permissions granted by a ClusterRole apply across the entire cluster, you can use ClusterRoles to control access to different kinds of resources than you can with Roles. These include:

  • Cluster-scoped resources such as Nodes
  • Non-resource Endpoints such as /healthz
  • Namespaced resources across all Namespaces (for example, all Pods across the entire cluster, regardless of Namespace)

Assigning Roles using RoleBindings or ClusterRoleBindings

After creating a Role or ClusterRole, you assign it to a user or group of users by creating a RoleBinding or ClusterRoleBinding. Users and groups are called subjects, and can be any of the following:

Subject type Value for kind Value for name
Google Cloud user account User Google Cloud registered email address
Kubernetes service account ServiceAccount The name of a Kubernetes ServiceAccount object in the cluster
Cloud IAM service account User Automatically generated Cloud IAM service account email address
G Suite Google Group address (Beta) on a verified domain Group Email address of a Google Group that is itself a member of the Google Group gke-security-groups@yourdomain.com

The following RoleBinding grants the pod-reader Role to a user, a Kubernetes service account, a Cloud IAM service account, and a Google Group:

kind: RoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: pod-reader-binding
  namespace: accounting
subjects:
# Google Cloud user account
- kind: User
  name: janedoe@example.com
# Kubernetes service account
- kind: ServiceAccount
  name: johndoe
# Cloud IAM service account
- kind: User
  name: test-account@test-project-123456.google.com.iam.gserviceaccount.com
# G Suite Google Group
- kind: Group
  name: accounting-group@example.com
roleRef:
  kind: Role
  name: pod-reader
  apiGroup: rbac.authorization.k8s.io

API Usage and Examples

For complete information on using the Kubernetes API to create the necessary Role, ClusterRole, RoleBinding, and ClusterRoleBinding objects for RBAC, see Using Role-Based Access Control Authorization in the Kubernetes documentation.

Troubleshooting and debugging

To debug issues with RBAC, the Admin activity audit log, which is enabled on all clusters by default. If access to a resource or operation is denied due to lack of sufficient permissions, the API server logs an RBAC DENY error, along with additional information such as the user's implicit and explicit group membership. If you are using Google Groups for GKE, google groups appears in the log message.

Debugging issues with Google Groups integration

The following instructions enable you to view logs to validate if your clusters have been successfully configured to use Google Groups in RBAC rolebindings.

Prerequisites

Before you begin examining the logs, make sure:

  • You have not interacted with the cluster you want to test (for example, ran any kubectl commands) for at least one hour. Authentication is cached for one hour and you need to make sure the request gets logged when it happens.
  • You are a member of at least one of the groups included in gke-security-groups. This ensures some Google Groups information is populated in the logs.

Configuring logs

To use logs for debugging Google Groups with RBAC:

  1. Enable data access logging for your Google Cloud project. To enable the logging:

    1. In the Cloud Console, go to the Audit Logs page in the Cloud IAM menu.

      Go to the Audit Logs page

    2. In the table, select Kubernetes Engine API.

    3. In the Log Type menu, select:

      • Admin Read
      • Data Read
      • Data Write
    4. Click Save.

    For more information about enabling Audit Logging, see Configuring Data Access logs with the Cloud Console in the Cloud management tools documentation.

  2. Run a command using kubectl in the cluster. This can be as simple as kubectl create ns helloworld.

  3. Enter a custom query in the Logs Viewer page. To run the query:

    1. In the Cloud Console, go to the Logs Viewer page in the Logging menu.

      Go to the Logs Viewer page

    2. Click the arrow in the Query preview box at the top of the page.

    3. In the dropdown box that appears, copy and paste the following query:

      resource.type="k8s_cluster"
      resource.labels.location="cluster-region"
      resource.labels.cluster_name="cluster-name"
      protoPayload.resourceName="authorization.k8s.io/v1beta1/subjectaccessreviews"
      protoPayload.response.spec.user="email-address"
      

      Where:

      • cluster-region is your cluster's region or zone.
      • cluster-name is the name of your cluster.
      • email-address is the registered email address of your Google account.
    4. Select Run Query. You should see at least one result. If you do not, try increasing the time range.

    5. Select the cluster you want to examine.

    6. Click Expand nested fields.

    7. The field protoPayload.request.spec.group contains the groups where:

      • The groups are members of gke-security-group.
      • You are a member of the group.

      This list should match the set of groups you are a member of. If no groups are present, there might be an issue with how the groups are set up.

  4. Restore data access logging to previous settings to avoid further charges (if desired).

Limitations

The following sections describe interactions that might not seem obvious when working with Kubernetes RBAC.

Default discovery roles

Clusters are created with a set of default ClusterRoles and ClusterRoleBindings. Requests made with valid credentials are placed in the system:authenticated group, whereas all other requests fall into system:unauthenticated. Prior to Kubernetes version 1.14, both system:authenticated and system:unauthenticated grant the system:basic-user and system:discovery ClusterRoles by default.

The system:basic-user ClusterRole lets users to make SelfSubjectAccessReviews to test their permissions in the cluster. The system:discovery role lets users to read discovery APIs, which can reveal information about CustomResourceDefinitions added to the cluster.

As of Kubernetes 1.14, anonymous users (system:unauthenticated) will receive the system:basic-info-viewer ClusterRole instead, which grants read-only access to /healthz and /version APIs.

To see the API endpoints allowed by the system:discovery ClusterRole, run the following command:

kubectl get clusterroles system:discovery -o yaml

Forbidden error for service accounts on Google Cloud VM instances

The following error can occur when the VM instance does not have the userinfo-email scope:

Error from server (Forbidden): error when creating ... "role-name" is forbidden: attempt to grant extra privileges:...

For example, suppose the VM has cloud-platform scope but does not have userinfo-email scope. When the VM gets an access token, Google Cloud associates that token with the cloud-platform scope. When the Kubernetes API server asks Google Cloud for the identity associated with the access token, it receives the service account's unique ID, not the service account's email.

To authenticate successfully, either create a new VM with the userinfo-email scope or create a new role binding that uses the unique ID.

To create a new VM instance with the userinfo-email scope, run the following command:

gcloud compute instances create instance-name \
    --service-account service-account-email \
    --scopes userinfo-email

To create a new role binding that uses the service account's unique ID for an existing VM, perform the following steps:

  1. Identify the service account's unique ID:

    gcloud iam service-accounts describe service-account-email
    

    For example, the following output displays the uniqueId for the my-iam-account@somedomain.com service account:

    displayName: Some Domain IAM service account
    email: my-iam-account@somedomain.com
    etag: BwWWja0YfJA
    name: projects/project-name/serviceAccounts/my-iam-account@somedomain.com
    oauth2ClientId: '123456789012345678901'
    projectId: project-name
    uniqueId: '123456789012345678901'
    
  2. Create a role binding using the uniqueId of the service account:

    kubectl create clusterrolebinding clusterrolebinding-name \
      --clusterrole cluster-admin \
      --user unique-id
    

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