Implementing RBAC for Kubernetes Cluster

Overview

Configure Kubernetes Role-Based Access Control (RBAC) to enforce least-privilege access to cluster resources. This skill covers Role/ClusterRole design, RoleBinding configuration, service account security, namespace isolation, and audit logging for multi-tenant Kubernetes environments.

Objectives

• Design RBAC role hierarchy for multi-tenant clusters
• Create granular Roles and ClusterRoles for different personas
• Configure RoleBindings and ClusterRoleBindings with least privilege
• Secure service accounts and limit their default permissions
• Integrate RBAC with external identity providers (OIDC)
• Audit and monitor RBAC usage with Kubernetes audit logs

Key Concepts

RBAC API Objects

1. Role: Namespace-scoped permissions (pods, services, deployments within a namespace)
2. ClusterRole: Cluster-wide permissions (nodes, namespaces, PVs, CRDs)
3. RoleBinding: Grants Role to users/groups/serviceAccounts in a namespace
4. ClusterRoleBinding: Grants ClusterRole cluster-wide

Kubernetes RBAC Verbs

• get, list, watch: Read-only operations
• create, update, patch: Write operations
• delete, deletecollection: Destructive operations
• impersonate: Assume identity of another user
• escalate: Modify RBAC roles (highly privileged)
• bind: Create RoleBindings (highly privileged)

Persona-Based Access Model

• Cluster Admin: Full cluster management (limit to 2-3 people)
• Namespace Admin: Full control within assigned namespace
• Developer: Deploy and manage workloads in assigned namespace
• Viewer: Read-only access to namespace resources
• CI/CD Service Account: Deploy workloads, manage configmaps/secrets

Implementation Steps

Step 1: Disable Default Permissive Settings

1. Ensure --authorization-mode=RBAC is enabled on API server
2. Remove default cluster-admin bindings from non-admin users
3. Disable auto-mounting of service account tokens in pods
4. Restrict access to default service account in each namespace

Step 2: Create Custom Roles

# Developer Role - namespace scoped
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  namespace: app-team
  name: developer
rules:
- apiGroups: ["", "apps", "batch"]
  resources: ["pods", "deployments", "services", "configmaps", "jobs"]
  verbs: ["get", "list", "watch", "create", "update", "patch", "delete"]
- apiGroups: [""]
  resources: ["secrets"]
  verbs: ["get", "list"]  # read secrets but limit create/update
- apiGroups: [""]
  resources: ["pods/log", "pods/exec"]
  verbs: ["get", "create"]

Step 3: Bind Roles to Users/Groups

apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: developer-binding
  namespace: app-team
subjects:
- kind: Group
  name: "dev-team"
  apiGroup: rbac.authorization.k8s.io
roleRef:
  kind: Role
  name: developer
  apiGroup: rbac.authorization.k8s.io

Step 4: Secure Service Accounts

• Create dedicated service accounts per application
• Disable automountServiceAccountToken for pods that don't need API access
• Use projected service account tokens with audience and expiry
• Bind minimum required permissions to each service account

Step 5: OIDC Integration

1. Configure API server with OIDC flags (issuer-url, client-id, username-claim, groups-claim)
2. Map OIDC groups to Kubernetes groups in RoleBindings
3. Use short-lived tokens from OIDC provider
4. Configure kubectl with OIDC authentication plugin

Step 6: Audit and Monitoring

• Enable Kubernetes audit logging (audit-policy.yaml)
• Log all RBAC-related events (role creation, binding changes)
• Alert on ClusterRoleBinding creation/modification
• Monitor for privilege escalation attempts
• Regular review of who has cluster-admin access

Security Controls

Common Pitfalls

• Granting cluster-admin to CI/CD pipelines
• Using wildcard (*) verbs or resources in ClusterRoles
• Not restricting pods/exec which allows container shell access
• Leaving default service account with broad permissions
• Not auditing who can create RoleBindings (privilege escalation vector)

Verification

• [ ] All users authenticate via OIDC (no static tokens/certs)
• [ ] No unnecessary ClusterRoleBindings to cluster-admin
• [ ] Developers limited to their assigned namespaces
• [ ] Service accounts use least-privilege roles
• [ ] automountServiceAccountToken disabled by default
• [ ] Audit logging captures RBAC changes
• [ ] kubectl auth can-i validates expected permissions per persona