How Kyverno Simplifies Admission Control in Secure Clusters

Written By:
Founder & CTO
June 23, 2025

In modern Kubernetes-native application development, ensuring robust security, standardization, and governance is no longer optional, it’s a foundational requirement. As teams scale their infrastructure and multiple developers contribute to workloads, maintaining consistency and enforcing best practices becomes critical. This is where Kyverno, an open-source Kubernetes policy engine, shines. Kyverno simplifies admission control in secure clusters by providing a declarative and Kubernetes-native way of defining, managing, and auditing security and compliance policies.

Unlike traditional methods that often require writing complex logic or learning non-YAML policy languages like Rego (used in OPA/Gatekeeper), Kyverno allows developers and cluster operators to define mutating, validating, generate, and image verification policies using simple, readable YAML. This not only reduces the learning curve but also ensures policies can be versioned, tracked, and managed as code, bringing all the benefits of GitOps to security enforcement.

Let’s dive deeper into how Kyverno enables secure, scalable admission control workflows in Kubernetes environments and why it is a must-have tool for any team building secure Kubernetes clusters.

Why Admission Control Matters for Developers
Admission controllers are the gatekeepers of Kubernetes security

In Kubernetes, admission controllers are plugins that intercept API server requests before they are persisted in etcd. This provides a powerful opportunity to enforce security and compliance rules before the actual deployment happens. For example, preventing a pod from running with a privileged container or ensuring that all workloads have the correct team label are typical use cases for admission control.

For developers, this is essential because:

  • It enforces security standards early in the CI/CD pipeline.

  • It reduces back-and-forth between DevOps and dev teams.

  • It automates consistency without manual enforcement.

But the built-in admission controllers are limited in scope. You can’t easily write custom logic, and they’re not adaptable to evolving team structures or workflows. Kyverno addresses these limitations with a powerful, extensible framework that supports multiple policy types while remaining Kubernetes-native.

Native YAML Policies, No New Language to Learn
Writing Kubernetes policies should be intuitive and native

Most policy engines require writing custom logic in a separate DSL or query language. For instance, Open Policy Agent (OPA) uses Rego, a powerful but non-trivial language. This creates a steep learning curve for developers, especially those who just want to express simple rules.

Kyverno changes this by letting you write policies directly in YAML, the same format used for Kubernetes manifests. This means:

  • No additional abstraction layers

  • No switching between YAML and another language

  • Policies that are self-documenting and readable

  • Easy onboarding for developers already familiar with Kubernetes

This makes Kyverno the most developer-friendly Kubernetes admission controller, dramatically improving the adoption rate across teams and reducing policy misconfiguration errors.

Four Key Policy Types in Action

Kyverno operates with four major types of policies, each offering different controls to manage how Kubernetes resources are created, modified, and validated.

Validate: Enforce structure and standards

Validation policies are used to ensure that Kubernetes resources meet specific criteria before they are allowed into the cluster. For example:

  • Ensuring labels like app, team, or environment are always present.

  • Verifying container security contexts, such as disallowing privileged: true.

  • Blocking the use of images from public registries.

By implementing these validation rules, Kyverno ensures every resource conforms to the organization’s operational and security standards. This shifts compliance checks left, right into the deployment phase.

Mutate: Automate resource transformations

Mutating policies allow you to modify resource definitions automatically during admission. Common use cases include:

  • Adding missing labels (e.g., owner: team-x)

  • Injecting resource limits and requests

  • Adding sidecar containers (e.g., for logging or monitoring)

  • Standardizing annotations or security policies

These mutations ensure configuration consistency across environments without burdening developers to manually include boilerplate in every manifest. It also dramatically reduces errors and saves time.

Generate: Enable self-service and automation

Generate policies are powerful tools for automating Kubernetes resource creation based on triggers. Examples:

  • Auto-create a ConfigMap or Secret when a new namespace is created

  • Generate RBAC rules for newly onboarded teams

  • Provision default NetworkPolicies for namespaces

These features empower self-service capabilities while maintaining tight control over the resources generated. They are especially useful in multi-tenant Kubernetes environments, where tenant isolation and automation go hand-in-hand.

verifyImages: Ensure container image integrity

The verifyImages policy allows Kyverno to integrate with container image signing tools like Cosign, Notary, or Sigstore, enforcing policies such as:

  • Only allow signed images

  • Reject images missing SBOM metadata

  • Accept images only from whitelisted registries

With growing concerns about software supply chain attacks, verifying images at the admission layer is an essential component of any secure Kubernetes setup. Kyverno enables this with minimal configuration, ensuring only trusted workloads are deployed.

How It Works Under the Hood

Kyverno runs as a set of Kubernetes controllers and admission webhooks:

The Webhook Controller

This is the primary interface between Kyverno and the Kubernetes API server. It registers Kyverno’s mutating and validating admission webhooks dynamically and ensures they are always up to date with the policy definitions.

The Policy Controller

Responsible for reconciling generate and mutate existing policies. It watches for resource creation events and applies the necessary transformations based on policies.

The Background Controller

Runs in the background to evaluate policies on existing resources in the cluster. This is useful for auditing and reporting.

The Cert Manager and Report Controller

Kyverno also ships with a certificate renewal manager for handling TLS certs required by webhooks and a report controller that generates PolicyReports and ClusterPolicyReports, which are CRDs summarizing policy compliance.

These components together ensure that Kyverno is highly available, performant, and self-healing, which is crucial for operating in production clusters.

Benefits for Developers
1. Faster onboarding & consistent configurations

Developers don’t need to memorize security policies or keep documentation handy. With Kyverno, policies are enforced automatically, and any resource that violates them gets blocked with meaningful feedback.

This accelerates onboarding for new team members and ensures consistent configuration across the team without needing to manually check every YAML file.

2. Automated fixes with minimal friction

Kyverno’s mutating policies auto-correct misconfigured resources. Developers can focus on writing core business logic while Kyverno fills in the gaps, resource limits, labels, annotations, and more.

This drastically reduces friction and helps maintain clean, production-ready manifests with zero manual overhead.

3. Fail early, fail fast

Kyverno validates resources during the admission phase. Any misconfigured or insecure resources are denied entry into the cluster immediately.

This "fail-fast" behavior allows developers to catch mistakes early in the pipeline, rather than debug production issues later. It also aligns perfectly with GitOps and CI/CD practices.

4. Securing the software supply chain

With verifyImages, Kyverno can enforce strict policies about container provenance, ensuring only signed, verified images from trusted registries are deployed.

This significantly mitigates risks from image tampering or untrusted sources, two common vectors in Kubernetes security breaches today.

5. Safe rollout with audit mode

You can apply policies in audit mode, which doesn’t block requests but still logs violations. This is ideal for testing policies in production-like environments before enforcing them.

It also provides a gradual, non-disruptive path to tightening security controls across workloads.

6. Multi-tenant cluster support and self-service

In clusters shared by multiple teams or environments, Kyverno allows defining namespace-scoped policies and even auto-generates RBAC or default workloads when a team is onboarded.

This supports a zero-touch onboarding experience while maintaining strict boundaries and governance.

7. Extends Kubernetes Pod Security Admission (PSA)

Kyverno doesn't replace PSA, it extends it. While PSA focuses on enforcing Pod Security Standards, Kyverno can define fine-grained, custom policies beyond those standards: annotations, labels, config values, image registries, and more.

8. Context-aware, developer-centric policies

Kyverno supports context-aware variables, like the user who submitted a request or the name of the target namespace. This enables sophisticated policies like:

  • Only devs from team-x can create workloads in team-x namespace

  • Block production deploys from non-admin users

  • Enforce specific standards based on labels or annotations

Kyverno vs Traditional Methods

Before Kyverno, teams had to choose between:

  • Manual enforcement: Relying on human diligence, error-prone and not scalable.

  • Kubernetes built-in admission controllers: Rigid and not customizable.

  • OPA/Gatekeeper: Powerful, but requires deep knowledge of Rego and non-YAML syntax.

Kyverno finds a perfect middle ground: no new language, YAML-native, highly flexible, and extensible. It aligns with existing Kubernetes workflows and works out-of-the-box with GitOps, CI/CD, and monitoring tools.

Size-Efficient Yet Powerful

Kyverno is lightweight, with container images under 100MB, and it avoids running heavyweight services or databases. It uses controller patterns familiar to Kubernetes and scales well with increased policy count and cluster size.

Even with hundreds of active policies, Kyverno maintains low memory and CPU usage, making it perfect for both small developer clusters and large-scale production workloads.

A Developer’s Journey With Kyverno
  1. Install Kyverno using Helm or YAML manifests.

  2. Define policies using YAML, start with label validation or restrict image registries.

  3. Apply them in audit mode to test policy effects.

  4. Observe violations via kubectl get policyreport -A or through Lens/ArgoCD dashboards.

  5. Gradually move to enforce mode for production-grade gating.

  6. Integrate into CI/CD workflows using kyverno test CLI and policy-as-code.

Real-World Testimonials

Developers on GitHub and Reddit regularly praise Kyverno’s simplicity:

“We replaced 90% of our Gatekeeper policies with Kyverno in a week. The YAML-native approach saved hours of onboarding.”

“Our entire platform team runs Kyverno policies to enforce team-specific limits and RBAC, without writing a line of Rego.”

Kyverno is also used in cloud-native platforms like SpectroCloud, Loft.sh, and is part of the CNCF sandbox, proving its adoption and reliability in real-world environments.

Potential Caveats and Best Practices
  • Run multiple Kyverno replicas for high availability.

  • Start policies in audit mode to validate without breaking things.

  • Use namespaceSelectors and resource filters to limit performance impact.

  • Keep policies versioned and tested just like application code.

Adoption Roadmap for Developers
  1. Phase 1: Install Kyverno in non-production clusters.

  2. Phase 2: Write baseline validation policies (labels, security context).

  3. Phase 3: Introduce mutate and generate policies.

  4. Phase 4: Enable verifyImages for signed images.

  5. Phase 5: Integrate into CI/CD for policy testing.

  6. Phase 6: Enforce across production clusters gradually.

Conclusion

Kyverno is more than just a policy engine, it’s a powerful security framework for Kubernetes clusters. It simplifies complex admission control use cases with native YAML policies that are easy to adopt, audit, and manage. For developers, it reduces configuration burden, enforces consistency, and prevents vulnerabilities early in the deployment cycle.

Whether you're building secure multi-tenant environments or enforcing container best practices, Kyverno enables secure, scalable, and developer-friendly Kubernetes clusters, with minimal friction and maximum control.