Access control management becomes more challenging as your Kubernetes journey grows. A formal authorization strategy may not be necessary in a small cluster with a few team members, but as the team grows, a structured approach is necessary to guarantee controlled and secure access.

‍

In order to keep things simpler early in your Kubernetes adoption, it's typical to provide everyone on the team with cluster admin capabilities. Nevertheless, there are inherent security dangers with this strategy. It's not necessary for every user to have full ability to add, edit, and remove resources. Implicit permissions can soon become a liability as the number of team members, applications, and cluster nodes increases.

‍

Role-Based Access Control, or RBAC, in Kubernetes, is essential for controlling resource access inside the cluster. Without RBAC there’s a high risk of compromising integrity and security of apps, data, and infrastructure by any user with cluster access.

In this article, we will discuss the core concepts of RBAC framework and best practices to implement RBAC policies effectively. 

Authentication and Authorization

Authentication and authorization are fundamental concepts in implementing the RBAC framework within Kubernetes. Authentication verifies the identity of people, services, or components trying to access the Kubernetes cluster. A variety of authentication methods, such as client certificates, bearer tokens, and authentication providers like LDAP, OAuth, or OpenID Connect, are supported by Kubernetes. Kubernetes relates the verified identity to a specific user or service account. Authorization on the other hand gives access to resources. After an entity has successfully authenticated, Kubernetes RBAC determines which resources and actions it is allowed to access within the cluster. RBAC rules, which specify roles, role bindings, and permissions, are used to handle authorization. 

‍

While authorization establishes what actions and resources those authorized entities can access based on preset roles and permissions, authentication verifies the identity of entities accessing the cluster, making sure they are authentic users. According to the least privilege concept, authentication and authorization work together to guarantee restricted and safe access to Kubernetes resources.

User and user group

Users and user groups are a vital component of Kubernetes RBAC (Role-Based Access Control), which defines permissions for access inside the cluster. Individual entities, such as users or service accounts, that need access to the cluster are represented as users in Kubernetes RBAC. Every user has an identity that is specific to them, which is usually verified by external identity providers, client certificates, or bearer tokens. Permissions are assigned to users according to their roles and role bindings.

‍

Groups are sets of users who have similar roles or characteristics. Grouping users together to streamline permission management is possible with Kubernetes RBAC. These groups can be tied to roles, which allows for the efficient and consistent assignment of permissions among several users with similar access needs.

Role and role binding

Role and Role bindings are used to grant permissions to users and user groups. In Kubernetes RBAC, a role is a set of rules that govern what can be done and what can't be done on particular resources in the cluster. A role's scope is limited to a certain namespace, or in the case of cluster roles, it covers the entire cluster. Role bindings link roles to specific users, groups, or service accounts. They create the connection between an entity that ought to have certain permissions and a role. Administrators can assign roles to individuals or groups and allow them to access resources by setting up role bindings.

Cluster role and clusterrole binding

Cluster role and clusterrole binding manage permissions throughout the clusters. A ClusterRole is a collection of rules that specify which users are allowed to access and manipulate resources at the cluster level. ClusterRoles are applicable throughout the whole Kubernetes cluster, in contrast to Roles, which are limited to a particular namespace. They specify rights for a variety of resources, including services, namespaces, nodes, and more. Administrators have the ability to construct ClusterRoles, which offer a worldwide scope for permissions.

<pre class="codeWrap"><code>apiVersion: v1
kind: ClusterRole
metadata:#
name: secret-reader
rules:
- apiGroups: [""]
resources: ["secrets"]
verbs: ["get", "watch", "list"]
</code></pre>

A ClusterRoleBinding links a ClusterRole throughout the cluster to a user, group, or service account. It gives particular entities the permissions specified in the ClusterRole. Across the cluster, ClusterRoleBindings can be used to define bespoke roles for different users or service accounts or to offer system administrators extensive access.

<pre class="codeWrap"><code>apiVersion: v1
‍kind: RoleBinding
metadata:
name: read-pods
namespace: default
subjects:
- kind:User
name: jane ‍
apiGroup: rbac.authorization.k8s.io
roleRef: ClusterRole
kind: Role
name: pod-reader
apiGroup: rbac.authorization.k8s.io
</code></pre>

Service accounts vs user account

In the Kubernetes RBAC framework, there are two types of accounts: user accounts and service accounts. Any entity outside the Kubernetes cluster represents a user account. It includes developers, administrators, or external systems. User accounts are authenticated through client certificates, bearer tokens, or other external identity providers. In Kubernetes service accounts grant permissions to pods running on clusters to communicate with other cluster resources and APIs. Service accounts use role binding or cluster binding to grant permission to specific roles or clusters role to the pod it represents.

RBAC rules

RBAC rules are an effective means for controlling resource access in Kubernetes clusters. These guidelines specify which individuals or groups are authorized to carry out particular tasks on particular resources. Because RBAC rules are written in a declarative language, they define the intended state of access rights rather than the actions necessary to get there. Because they are not dependent on the underlying infrastructure or authentication method, RBAC rules are therefore simpler to manage and maintain.

‍

There are three primary components of every RBAC rule:

Subject: It is the user or group to which the RBAC rule applies.

Resource: It includes services, namespace, pods, or other Kubernetes resources.

Verb: It is the activity on the resource that the user is permitted to carry out. A verb could be create, get, update, and delete.

‍

Let’s have an example where an RBAC rule grants the administrator group the permission to create pods in the production namespace:

<pre class="codeWrap"><code>kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1beta1
metadata:
  name: administrator
rules:
- apiGroups: [""]
  resources: ["pods"]
  verbs: ["create"]
</code></pre>

‍

According to this rule, only a set of users who are responsible for introducing new apps into the production environment are authorized. This way, we make sure they only have access to the resources they need to do their work and keep them from making unauthorized changes to other sections of the cluster by giving them particular rights.

‍

It is possible to nest RBAC rules inside other rules to produce a hierarchical structure. This enables you to assign authority to roles at a lower level and construct reusable permission sets. For instance, you can create a developer's role with the authority to create and update pods, and then a DevOps role with the same rights plus the power to remove pods.

Best practices for implementing RBAC framework in Kubernetes

To effectively utilize the power of RBAC rules in Kubernetes clusters, certain best practices should be adhered to:

• Give users, service accounts, or groups only the minimal amount of rights necessary for them to carry out their tasks in accordance with the principle of least privilege. Refrain from granting excessively broad permissions as this can cause security problems.
• Use namespaces to partition and isolate resources, and whenever possible, implement RBAC policies at the namespace level. This makes it easier to maintain distinct boundaries for access control and concern separation.
• Make sure that permissions need to be scoped to a particular namespace or the entire cluster. For permissions that are particular to a namespace, use Roles; for cluster-wide permissions, use ClusterRoles.
• As ClusterRoles provide wide rights for the entire cluster, it is best to avoid directly allocating them to specific individuals. For more precise control within namespaces, use RoleBindings instead.
• Avoid using wildcard (*) verbs in ClusterRoles since they allow resources to be accessed without limitation. Based on the real requirements, define exact verbs such as obtain, list, create, update, delete, etc.
• Make sure RBAC settings are regularly reviewed and audited to make sure they meet the demands of access control. Delete any out-of-date or unnecessary permissions to keep everything secure.
• When appropriate, apply role hierarchies and RBAC role aggregation.
• To make management easier and encourage reusability, group relevant permissions into roles.
• To offer contextual information and facilitate the administration and identification of roles and their objectives, apply labels and annotations to roles and role bindings.
• In non-production environments, thoroughly test RBAC configurations to ensure that the defined permissions function as expected and prevent unauthorized access.
• Completely document RBAC setups, including the justification for permission assignments and any exceptions that exist. Communicate the policies with all team members and interested entities.

Conclusion

To sum up, the RBAC framework is a powerful tool to ensure resource management and security in Kubernetes. By adhering to the RBAC rules and best practices regulated and secure access to Kubernetes clusters is possible.