OPA Gatekeeper - A policy enforcement tool for Kubernetes that leverages policy as code to ensure compliance with security standards. https://github.com/open-policy-agent/gatekeeper

OPA Gatekeeper is a powerful and customizable admission webhook for Kubernetes that leverages the Open Policy Agent (OPA) to enforce policies and strengthen governance within your Kubernetes clusters. It allows you to define and manage policies as code, ensuring compliance and security across your Kubernetes resources.

• **Policy as Code:** Gatekeeper uses the Rego policy language to define policies, enabling you to express complex rules and constraints in a declarative and human-readable format.
• **Custom Resource Definitions (CRDs):** It introduces CRDs like `ConstraintTemplate` and `Constraint` into Kubernetes, providing a Kubernetes-native way to define and manage policies.
• **Admission Webhooks:** Gatekeeper acts as a validating admission webhook, intercepting requests to the Kubernetes API server and evaluating them against your defined policies before allowing or denying the operation.
• **Audit Functionality:** It periodically audits your cluster to identify existing resources that violate your policies, enabling proactive compliance enforcement and remediation.
• **External Data Support:** Gatekeeper can integrate with external data sources, such as configuration management systems or security databases, to enrich policy decisions with additional context.

• **Enhanced Security and Compliance:** Gatekeeper enforces consistent security and compliance standards across your Kubernetes clusters, preventing unauthorized or misconfigured deployments.
• **Centralized Policy Management:** It provides a centralized location for defining and managing policies, ensuring that they are applied consistently across your environment.
• **Declarative Approach:** Gatekeeper's use of Rego and CRDs makes it easy to define and manage policies in a declarative way, promoting clarity and maintainability.
• **Proactive Enforcement:** Admission webhooks prevent non-compliant resources from being created or modified, ensuring policy adherence from the start.
• **Auditing and Remediation:** The audit functionality helps identify existing resources that violate policies, enabling you to take corrective actions.

1. **ConstraintTemplate Definition:**

```yaml apiVersion: templates.gatekeeper.sh/v1beta1 kind: ConstraintTemplate metadata:

 name: k8srequiredlabels

 crd:
   spec:
     names:
       kind: K8sRequiredLabels
 targets:
   - target: admission.k8s.gatekeeper.sh
     rego: ]] | [[
       package k8srequiredlabels

       violation[{"msg": msg}] {
         provided := {key ]] | [[ input.review.object.metadata.labels[key]}
         required := {key ]] | [[ key := input.parameters.labels[_]}
         missing := required - provided
         count(missing) > 0
         msg := sprintf("you must provide labels: %v", [missing])
       }

This ConstraintTemplate defines a policy that requires specific labels to be present on Kubernetes resources.

2. **Constraint Definition:**

```yaml apiVersion: constraints.gatekeeper.sh/v1beta1 kind: K8sRequiredLabels metadata:

 name: require-labels-on-namespace

 match:
   kinds:
     - apiGroups: [""]
       kinds: ["Namespace"]
 parameters:
   labels: ["environment"]

This Constraint enforces the “k8srequiredlabels” policy, requiring the “environment” label to be present on all Namespace resources.

• **OPA Gatekeeper GitHub Repository:** s://github.com/open-policy-agent/gatekeeper(https://github.com/open-policy-agent/gatekeeper)
• **OPA Gatekeeper Documentation:** s://open-policy-agent.github.io/gatekeeper/website/docs/(https://open-policy-agent.github.io/gatekeeper/website/docs/)