Understanding Kubernetes Authentication and Authorization
Tags: kubernetes, cloudnative, security
Published: 2023-11-30 15:24:21

Setting up user permissions properly in Kubernetes involves understanding and effectively using Kubernetes' Role-Based Access Control (RBAC) system. RBAC in Kubernetes allows you to regulate access to resources in the cluster based on the roles of individual users or groups of users. Here's a step-by-step guide to setting up user permissions:

### 1. Understand Kubernetes Authentication and Authorization

Firstly, understand that Kubernetes separates authentication (verifying who you are) from authorization (determining what you can do):

- **Authentication**: You can authenticate users via certificates, tokens, basic auth, external identity providers like LDAP, etc.
- **Authorization**: Once authenticated, authorization determines what actions the user can perform. Kubernetes uses RBAC for authorization.

### 2. Define Users and Groups

In Kubernetes, users are not created through the Kubernetes API but should be managed externally. For instance, you can have:

- **Service Accounts** for processes in pods.
- **Normal Users** managed externally (e.g., via an identity provider).
- **Groups**, which are collections of users.

### 3. Use Role and ClusterRole

- **Role**: A `Role` in Kubernetes is used to grant permissions within a specific namespace. It contains rules that represent a set of permissions.
- **ClusterRole**: A `ClusterRole` is like a Role, but for the entire cluster. It's useful for granting permissions for non-namespaced resources (like nodes) or for namespaced resources across all namespaces.

### 4. Create RoleBindings and ClusterRoleBindings

- **RoleBinding**: A `RoleBinding` grants the permissions defined in a Role to a user or set of users. It applies only within a specific namespace.
- **ClusterRoleBinding**: A `ClusterRoleBinding` grants the permissions defined in a ClusterRole to a user or set of users cluster-wide.

### 5. Define Roles and Bindings

Create YAML files to define `Roles`/`ClusterRoles` and `RoleBindings`/`ClusterRoleBindings`. For example:

#### Role Example

```yaml
kind: Role
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  namespace: default
  name: pod-reader
rules:
- apiGroups: [""]
  resources: ["pods"]
  verbs: ["get", "watch", "list"]
```

#### RoleBinding Example

```yaml
kind: RoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: read-pods
  namespace: default
subjects:
- kind: User
  name: jane
  apiGroup: rbac.authorization.k8s.io
roleRef:
  kind: Role
  name: pod-reader
  apiGroup: rbac.authorization.k8s.io
```

### 6. Apply the Configuration

Apply these configurations using `kubectl apply -f <filename>.yaml`.

### 7. Test the Permissions

Verify that the permissions are correctly set up by attempting to perform operations in the cluster as the specified users.

### 8. Regular Audits and Updates

Regularly audit and update the permissions to ensure they align with current operational requirements and security best practices.

### 9. Consider Using a Management Tool

For complex environments, consider using a Kubernetes management tool that offers a more user-friendly interface for managing roles and permissions.

Remember, proper setup of user permissions is crucial for the security of your Kubernetes cluster. Always follow the principle of least privilege, granting users only the permissions they need to perform their tasks.