Kyverno Best Practices: Policy Management That Scales in Kubernetes

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Avoid the pitfalls. Do policy-as-code the right way.

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Why Kyverno?

Kyverno has evolved as the first choice Kubernetes-native policy engine for teams to be able to validate, mutate, and secure workloads without escaping YAML. It’s flexible, CEL-powered, and integrates smoothly into the admission control, CI/CD pipelines, and compliance frameworks.

However, the very flexibility that is the strength is also the Achilles’ heel of using such a solution — the misfunction of the policies, the surplus of reports, the actually under-performant that leads to significant performance costs, and the policy sprawl are the exact problems in the production clusters.

Rather than only doing things correctly, this guide demonstrates how to be more efficient with Kyverno.

1. Start with Validation Before Mutation

Mutation policies are powerful but risky if applied prematurely. They can auto-correct things in ways you may not intend.

Best Practice:
Start with ValidatingPolicy (or traditional ClusterPolicy with validation rules) to enforce standards. Once teams are aligned, introduce mutation as a follow-up—not the first step.

2. Use CEL Expressions Over Pattern Matching

While validate.pattern works, CEL is more expressive and maintainable, especially for complex logic.

Use:

expression: "object.spec.replicas <= 5"

Avoid deep pattern trees that become brittle and hard to debug:

pattern:
  spec:
    replicas: "<= 5"

3. Secure the Supply Chain with ImageValidatingPolicy

Don’t trust that an image is what it claims. Use ImageValidatingPolicy to:

• Verify image signatures
• Validate SBOMs and attestations
• Lock down allowed registries

Example:

expression: >-
  images.containers.map(image, verifyImageSignatures(image, [attestors.notary])).all(e, e > 0)

Pair this with glob or regex to target only certain registries (ghcr.io/*, gcr.io/company/*, etc.).

4. Scope Policies with match and exclude—Always

Don’t write policies that blanket the whole cluster unless you really mean to. Use matchConstraints, resourceRules, namespaceSelector, and exclude to limit impact and reduce false positives.

Best Practice:

match:
  namespaces:
    - "production"

5. Shift-Left with the Kyverno CLI

Run policy checks before you deploy. Kyverno’s CLI can validate:

• Kubernetes manifests
• Helm templates
• Dockerfiles (in JSON)

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6. Monitor Policy Reports (Don’t Ignore Violations)

Use PolicyReport resources and hook them into:

• Policy Reporter
• Dashboards like Grafana/Loki
• Alerts via Slack/Webhooks

Don’t just enforce — observe.

7. Use PolicyException Strategically

Hard-blocking every violation isn’t always practical. Use PolicyException CRDs for targeted, CEL-filtered overrides.

Example:

expression: "object.metadata.name == 'legacy-job'"

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8. Cache and Reuse With GlobalContext

For performance and policy composability, Kyverno supports caching lookups in a shared GlobalContext. Useful for:

• Allowed registry lists
• Team-specific constraints
• External API results (with HTTP library)

Tip: Avoid repeated lookups in each rule — cache it once, reuse it everywhere.

9. Keep Policies Modular and Focused

Don’t cram 10 rules into one policy. It becomes unmanageable fast.

Split policies by:

• Function (e.g., restrict-replicas, enforce-labels)
• Scope (e.g., dev-only, prod-only)
• Type (ValidatingPolicy, ImageValidatingPolicy, etc.)

Modular = testable, readable, maintainable.

10. Lock Kyverno Itself Down

Yes — Kyverno needs guardrails too.

Best Practice:

• Run it in a dedicated namespace (kyverno-system)
• Set strict RBAC and PodSecurityPolicies for its controllers
• Monitor its logs and webhook performance (e.g., timeout errors)

Bonus: Helm Charts and GitOps Tips

If you’re managing Kyverno via GitOps (ArgoCD, Flux):

• Use Helm’s values.yaml to pre-load policies
• Separate policy lifecycle from application rollout
• Version-control your policies like code (because they are)

Final Thoughts

Kyverno gives teams massive power over their Kubernetes environments — but it pays to be intentional. Use the new policy types (ValidatingPolicy, ImageValidatingPolicy), enforce with CEL, scope precisely, and always monitor the results.

With the right practices, Kyverno becomes more than a policy engine — it becomes a foundation for secure, resilient, compliant infrastructure.

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