Hardening Kubernetes Admission Controllers for Multi-Tenant Clusters

Multi-Tenancy Raises the Stakes When dozens of teams deploy to the same Kubernetes control plane, misconfigured workloads become a shared risk. Admission controllers are your gatekeepers, ensuring only compliant resources enter the cluster. Without them, privilege escalation and data exfiltration become inevitable.

Designing Policy Layers Start with built-in controllers like `NamespaceLifecycle` and `ResourceQuota`, then layer on Open Policy Agent (OPA) Gatekeeper or Kyverno for custom rules. Define policies that restrict hostPath mounts, enforce read-only root file systems, and require image provenance tags. Use dry-run mode to test new rules before enforcing them cluster-wide.

Continuous Compliance Version-control your policies and deploy them via GitOps so drift becomes visible. Integrate policy checks into CI pipelines to catch violations before they hit the cluster. Export admission decisions to your SIEM—denied requests often reveal threat actor reconnaissance or developer shortcuts.

Handling Exceptions Create a structured exemption workflow with expiration dates, documented business justification, and compensating controls. Automate reminders when exceptions near expiry, forcing teams to fix the underlying issue.

Final Outcome Strong admission control gives platform teams confidence to scale multi-tenant clusters without sacrificing security. Treat policies as living code and they will keep pace with your deployments.