RBAC in Kubernetes is implemented using Policies that define the permissions, and Subjects, which are the entities to which these permissions are granted. Policies are defined through Roles and ClusterRoles, while Subjects can be Users, Groups, or ServiceAccounts, bound to the roles using RoleBindings or ClusterRoleBindings.
In this article:
- Why Is RBAC Important for Kubernetes?
- Core Components of Kubernetes RBAC
- How to Use Kubernetes RBAC
- Common Challenges and Solutions in Kubernetes RBAC
- Best Practices for Using Kubernetes RBAC
Why Is RBAC Important for Kubernetes?
Granular Access Control
The power of RBAC lies in its granular control over Kubernetes resources. RBAC allows you to specify exactly what actions a user can perform, and on what resources. This makes it possible to tailor access rights to the specific needs of each user or group, preventing unnecessary access and reducing the risk of security breaches. For instance, you can allow a user to view the status of Pods in a specific namespace, but not to create or delete them.
Improved Security
In addition to providing granular control, RBAC significantly improves the security of your Kubernetes system. By limiting access based on the principle of least privilege, RBAC minimizes the potential for unauthorized or harmful actions. This is especially important in a distributed system like Kubernetes, where a security breach in one part of the system can potentially impact the entire cluster.
Access Auditing
Kubernetes RBAC also enables robust access auditing. With RBAC, you can track exactly who has access to what resources, and what actions they can perform. This makes it easier to conduct security audits, troubleshoot issues, and ensure compliance with security policies and regulations.
Simplifies Management
Finally, RBAC simplifies the management of access rights in Kubernetes. By grouping users into Roles and ClusterRoles, you can manage access rights in a more organized and scalable way. This is particularly useful in large or complex Kubernetes deployments, where managing individual user rights would be impractical or impossible.
Related content: Read our guide to Kubernetes architecture
Core Components of Kubernetes RBAC
Here are the main components that make up the Kubernetes RBAC mechanism.
Role and ClusterRole
In Kubernetes RBAC, permissions are defined through two types of objects: Roles and ClusterRoles. A Role defines permissions within a specific namespace, while a ClusterRole defines permissions cluster-wide. Both types of roles allow you to specify a set of rules that define what actions can be performed on which resources.
RoleBinding and ClusterRoleBinding
To grant the permissions defined in a Role or ClusterRole to a user, group, or ServiceAccount, you use another set of objects: RoleBindings and ClusterRoleBindings. A RoleBinding grants the permissions defined in a Role to a user within a specific namespace. In contrast, a ClusterRoleBinding grants the permissions defined in a ClusterRole to a user across the entire cluster.
ServiceAccounts
ServiceAccounts are a special type of user in Kubernetes, designed to be used by processes running inside Pods. Like regular users, ServiceAccounts can be assigned Roles and ClusterRoles using RoleBindings and ClusterRoleBindings. This allows you to control the permissions of your applications in the same granular and secure way as your human users.
Learn more in our detailed guide to Kubernetes services
How to Use Kubernetes RBAC
Enabling RBAC
Kubernetes RBAC is typically enabled by default in most modern Kubernetes distributions. However, if you are using an older version or a custom Kubernetes setup, you may need to manually enable RBAC. This is done by starting the Kubernetes API server with the --authorization-mode=RBAC flag.
Creating a Role
Creating a role in Kubernetes involves defining a Role object in a YAML file. The Role object includes the API group, the resources, and the verbs (actions) that are allowed. For example, the following role only allows ‘get’ and ‘list’ actions on pods in the core API group.
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
namespace: default
name: pod-reader
rules:
- apiGroups: [""]
resources: ["pods"]
verbs: ["get", "list"]Once you have defined the Role object, you can create the role in your Kubernetes cluster by running the following command (assuming the YAML file was saved as role.yaml):
kubectl apply -f role.yaml
Keep in mind that roles in Kubernetes are namespace-specific. This means that the permissions granted by a role apply only within a specific namespace. If you want to grant permissions across all namespaces, you will need to create a ClusterRole.
Creating a ClusterRole
A ClusterRole is similar to a Role, except that it grants permissions across all namespaces in your Kubernetes cluster. This is useful for granting permissions to cluster-wide resources such as nodes and persistent volumes.
Creating a ClusterRole involves defining a ClusterRole object in a YAML file. Like a Role object, a ClusterRole object includes the API group, the resources, and the verbs that are allowed. Here is an example of a ClusterRole:
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
name: pod-reader-global
rules:
- apiGroups: [""]
resources: ["pods"]
verbs: ["get", "list"]You can create the ClusterRole in your Kubernetes cluster by running the following command (assuming the YAML file was saved as clusterrole.yaml):
kubectl apply -f clusterrole.yaml
Creating a RoleBinding
A RoleBinding is an object that binds a Role to a subject. The subject can be a user, a group, or a service account. The RoleBinding grants the permissions defined in the Role to the subject.
To create a RoleBinding, you define a RoleBinding object in a YAML file. For example:
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
name: read-pods
namespace: default
subjects:
- kind: User
name: "janedoe"
apiGroup: rbac.authorization.k8s.io
roleRef:
kind: Role
name: pod-reader
apiGroup: rbac.authorization.k8s.ioYou can create the RoleBinding in your Kubernetes cluster by running this command (again, assuming the YAML file is saved as rolebinding.yaml):
kubectl apply -f rolebinding.yaml
Once the RoleBinding is created, the subject will have the permissions granted by the Role in the namespace where the RoleBinding is created.
Creating a ClusterRoleBinding
A ClusterRoleBinding is similar to a RoleBinding, but it binds a ClusterRole to a subject. This grants cluster-wide permissions to the subject.
You define a ClusterRoleBinding in a YAML file, similar to a RoleBinding. For example:
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
name: read-pods-global
subjects:
- kind: User
name: "janedoe"
apiGroup: rbac.authorization.k8s.io
roleRef:
kind: ClusterRole
name: pod-reader-global
apiGroup: rbac.authorization.k8s.ioTo create the ClusterRoleBinding run this comment (assuming the YAML file is saved in clusterrolebinding.yaml):
kubectl apply -f clusterrolebinding.yaml
Common Challenges and Solutions in Kubernetes RBAC
Complex Permission Mapping
The first challenge that many administrators face with Kubernetes RBAC is the complexity of permissions. Kubernetes, by design, offers a granular level of access control, which can quickly become overwhelming. The way roles, role bindings, and cluster role bindings work together to control who can access what in a cluster is a complex matrix that requires careful management.
To simplify this process, start by mapping out your application’s functionalities and the necessary permissions for each role. This will provide a clear overview of the permissions matrix for your application and help you manage the roles more effectively.
RBAC Misconfigurations
RBAC misconfigurations are another common issue. These can occur when permissions are not properly set, leading to either excessive permissions or insufficient permissions. Both scenarios pose significant risks. Excessive permissions can lead to unauthorized access or actions, while insufficient permissions can hinder the functionality of your application.
To avoid RBAC misconfigurations, ensure you thoroughly understand the principle of least privilege (more on this later) and apply it diligently. Regular auditing of your RBAC configurations and rigorous testing can also help identify and rectify misconfigurations. In addition, it is critical to test TBAC configurations in a test environment before deploying in production.
Read our blog post: First-Ever Attack Leveraging Kubernetes RBAC to Backdoor Clusters
Managing ServiceAccount Credentials
ServiceAccounts in Kubernetes are meant to provide an identity for processes that run in a pod. However, managing these ServiceAccount credentials can become a challenge as your applications grow and scale.
To manage ServiceAccount credentials effectively, consider automating the process where possible. Kubernetes provides several tools and APIs that can help automate the management of ServiceAccount credentials. These tools will not only save you time but also reduce the risk of human error.
It is critical to regularly review and audit the use of ServiceAccounts. They should be refreshed periodically and must be deactivated as soon as they are no longer needed.
Difficulty Troubleshooting Access Issues
Lastly, troubleshooting access issues in Kubernetes RBAC can be a complex task due to the granularity of the permissions and roles. Often, you may find yourself sifting through numerous policies and bindings to identify the root cause of an access issue.
To simplify troubleshooting, consider using logging and monitoring tools that provide a comprehensive view of your access control system. These tools can help identify patterns and pinpoint issues more quickly and accurately.
Best Practices for Using Kubernetes RBAC
1. Principle of Least Privilege
The principle of least privilege is a security concept that requires that a user be given the minimum levels of access necessary to complete his/her job functions. This principle is crucial in Kubernetes RBAC to prevent unauthorized access and actions.
To implement this principle, start by defining the necessary permissions for each role in your application. Ensure that each role only has access to the resources it needs to function and nothing more.
2. Regularly Audit Permissions
Auditing your Kubernetes RBAC configurations regularly is another best practice. This can help identify and fix misconfigurations, excessive permissions, and other potential security risks.
You can automate the auditing process using Kubernetes’ Audit Logging feature. This feature allows you to log all API requests, making it easier to monitor and audit your RBAC configurations.
3. Use Namespaces Wisely
Namespaces in Kubernetes are a way to divide cluster resources between multiple users. Using namespaces wisely can help manage your access control more effectively.
Consider using namespaces to isolate different environments (e.g., development, staging, production) or different teams within your organization. This can help prevent accidental or unauthorized access across different parts of your application.
4. Limit Use of ClusterAdmin
The ClusterAdmin role in Kubernetes has unrestricted access to the entire cluster. While this role can be useful for administrative tasks, it poses significant security risks if misused.
As a best practice, limit the use of the ClusterAdmin role. Instead, create specific roles with the necessary permissions for each task or function in your application.
