Gatekeeper 1.0 Alpha: Policy Guardrails for Kubernetes

Introduction

Google, Microsoft, and the OPA community unveiled Gatekeeper 1.0 alpha on July 17, 2019, uniting Open Policy Agent with Kubernetes admission controls. Gatekeeper turns compliance rules into versioned CRDs that cluster operators can manage alongside application manifests.

Architecture at a Glance

• ConstraintTemplates: Define reusable Rego policies paired with OpenAPI schemas for parameters.
• Constraints: Instantiate templates per namespace, environment, or workload type.
• Mutation Webhooks (alpha): Auto-correct manifests by injecting defaults before they hit the API server.

Why It Matters

1. Declarative Guardrails: Store policies in Git, review them, and roll them out with Argo CD or Flux.
2. Audit Mode: Scan live resources for drift without blocking deploys, easing adoption.
3. Status Feedback: Constraint CRDs surface violations with detailed error messages and remediation hints.

Common Use Cases

• Enforce image provenance or disallow :latest tags.
• Require resource limits, labels, or PodSecurityPolicy equivalents.
• Govern multi-tenant clusters by pinning namespaces to allowed node pools.

Getting Started

kubectl apply -f https://raw.githubusercontent.com/open-policy-agent/gatekeeper/v1.0.0-alpha.1/deploy/gatekeeper.yaml
kubectl apply -f constrainttemplate-k8srequiredlabels.yaml
kubectl apply -f constraint-ns-must-have-team.yaml

Ship templates and constraints through CI to keep policy changes auditable.

Summary

Gatekeeper 1.0 alpha lays the groundwork for policy-as-code in Kubernetes, aligning security teams and platform engineers around the same Git-based workflows.