Policy as Code: Understand OPA and Kyverno for Kubernetes
Policy as code is the practice of defining security, compliance, and operational rules as code that can be automatically enforced across infrastructure instead of relying on manual reviews. In Kubernetes, this means every resource created in a cluster is evaluated against predefined policies before it is deployed, helping teams maintain consistent governance at scale. Rather than checking YAML files manually, policy engines validate configurations, enforce resource limits, restrict container images, and ensure compliance automatically.
Two of the most widely used tools for implementing policy as code are OPA (Open Policy Agent) and Kyverno. While both integrate with Kubernetes admission controllers, they take different approaches. OPA uses the Rego policy language and can enforce policies across Kubernetes, APIs, CI/CD pipelines, and other systems, making it ideal for organizations seeking a unified governance framework. Kyverno, by contrast, is Kubernetes-native and uses familiar YAML syntax, making it easier for platform teams already working with Kubernetes manifests.
As Kubernetes environments grow larger and more complex, automated policy enforcement has become essential for improving security, reducing configuration drift, and ensuring every deployment complies with organizational standards without slowing down development.
Policy as Code: OPA and Kyverno for Kubernetes
Policy as code is the practice of writing governance rules, security requirements, compliance standards, resource limits, naming conventions, as version-controlled, machine-readable code, rather than as documents that get manually reviewed. Just as infrastructure as code brought version control, automated testing, and repeatability to provisioning infrastructure, policy as code brings the same discipline to enforcing rules about how that infrastructure is used.
In a Kubernetes context, policy as code answers a specific question: how do you make sure every deployment, pod, or resource created in a cluster actually complies with your organisation's standards, automatically, without relying on a human reviewing every YAML file before it's applied? The two tools that dominate this space in 2026 are OPA (Open Policy Agent) and Kyverno, and understanding both is essential for any platform or security engineer working with Kubernetes governance.
Why Kubernetes Needs Policy as Code
Kubernetes enforces policy through admission controllers, components that intercept requests to the API server before an object is persisted, and can validate, mutate, or reject it. Kubernetes previously shipped a built-in policy mechanism called Pod Security Policies (PSPs), but these were removed in Kubernetes v1.25 and replaced with Pod Security Admission, a simpler kubernetes controller based on Pod Security Standards.
The problem is that Pod Security Admission only covers pod-level security settings, it can't enforce broader organisational policy like 'every image must come from an approved registry' or 'every Deployment must have resource limits set.' This gap is exactly why external policy as code tools like OPA and Kyverno remain essential, they plug into the same admission control mechanism but support far more flexible, custom policy logic across any Kubernetes resource type.
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What Is OPA (Open Policy Agent)?
OPA (Open Policy Agent) is an open-source, general-purpose policy engine, not built specifically for Kubernetes, but designed to enforce policy across many kinds of systems: microservices, CI/CD pipelines, API gateways, and Kubernetes among them. OPA was originally developed by Styra and is now a CNCF Graduated project, reflecting its maturity and widespread production adoption.
Open policy agent policies are written in Rego, a purpose-built declarative query language designed for expressing complex policy logic and data transformations. This general-purpose design is OPA's biggest strength: the same Rego policy logic that enforces a rule in Kubernetes can, in principle, be reused to enforce equivalent logic in other systems, giving organisations a single policy language across very different infrastructure layers.
OPA Gatekeeper: OPA as a Kubernetes Controller
OPA Gatekeeper is the project that adapts OPA specifically for Kubernetes, technically, it's a customisable Kubernetes admission webhook, functioning as a kubernetes controller that intercepts API requests and enforces Rego-based policy decisions before objects are persisted to the cluster.
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Constraint Templates define reusable policy logic in Rego, which can be parameterised and applied across multiple clusters
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Constraints are the actual policy instances, applying a given Constraint Template with specific parameters to enforce a rule
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Gatekeeper's audit subsystem periodically re-evaluates existing cluster resources against active policies, surfacing violations that existed before a policy was created
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Because Gatekeeper runs multiple pods to handle webhook and audit responsibilities separately, it typically consumes more CPU and memory than a comparably scoped Kyverno deployment
OPA Gatekeeper is the right entry point for opa gatekeeper adoption specifically when your team already has Rego expertise, or when policy reuse across non-Kubernetes systems is a genuine requirement, not just a nice-to-have.
What Is Kyverno?
Kyverno is a policy engine designed specifically for Kubernetes, unlike OPA, it was built from the ground up as a Kubernetes-native kubernetes controller, and Kyverno policies are themselves Kubernetes custom resources, manageable with kubectl and standard GitOps tooling like any other cluster object.
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Kyverno policies are written entirely in YAML, no new policy language to learn, which significantly lowers the onboarding curve for teams already comfortable with Kubernetes manifests
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Kyverno supports validation (block or warn on non-compliant resources), mutation (automatically modify resources to bring them into compliance), and generation (automatically create supporting resources, like default NetworkPolicies) as first-class policy types
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Kyverno typically runs as a single controller pod handling validation, mutation, and generation together, giving it a lighter operational footprint than Gatekeeper's multi-pod model
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Kyverno has moved from the CNCF Sandbox to CNCF Incubating maturity level, reflecting its growing production adoption
Kyverno's built-in mutation and generation capabilities are a genuine differentiator, where OPA Gatekeeper historically focused on validation and added mutation later through separate resources, Kyverno treats all three capabilities as native, equally first-class parts of the same policy definition.
Kyverno vs OPA Gatekeeper: The Real Differences
As of early 2026 (Kyverno 1.13, Gatekeeper 3.18), both projects have converged on feature parity for core Kubernetes admission-control workloads. The decision now comes down to fit, not raw capability.
| Dimension | Kyverno | OPA Gatekeeper |
|---|---|---|
| Policy language | Plain YAML, no new language | Rego, a dedicated policy language |
| Learning curve | Low, familiar to any Kubernetes user | Higher, Rego takes real time to learn |
| Mutation & generation | Native, first-class YAML policy types | Added later, via separate resources |
| Cross-platform reuse | Kubernetes-only | Rego reusable across APIs, CI/CD, Terraform |
| Operational footprint | Typically a single controller pod | Typically multiple pods (webhook + audit) |
| CNCF maturity | Incubating | Graduated |
| Best for | Teams wanting simplicity and fast onboarding | Teams needing complex logic or policy reuse beyond Kubernetes |
Neither tool is operationally bad, but Kyverno generally requires less specialised expertise to keep healthy in production, Gatekeeper's separate constraint template and constraint model, along with its independent audit subsystem, demands more careful operational handling.
CTA: Build Kubernetes Policy Automation with Confidence
Understanding the differences between OPA Gatekeeper and Kyverno is only the beginning. The real advantage comes from learning how to design, test, and enforce policy as code across Kubernetes environments using admission controllers, governance frameworks, and GitOps workflows. Develop the hands-on skills to secure production clusters with automated, scalable policy enforcement.
Writing a Policy in Each Tool
Seeing the same rule, require a resource limit on every container, written in both tools makes the language difference concrete.
Kyverno: YAML Policy
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The Kyverno version reads almost like plain Kubernetes YAML, declarative, pattern-based, no separate language. The OPA Gatekeeper version requires understanding Rego syntax and its rule-evaluation model, but that same Rego logic could, with adaptation, enforce an equivalent rule outside Kubernetes entirely, the trade-off between simplicity and cross-platform reuse in one side-by-side example.
Which Should You Choose in 2026?
For most teams standardising on a single policy as code tool purely for Kubernetes admission control, Kyverno is usually the easier choice in 2026, lower learning curve, native mutation and generation, and a lighter operational footprint. For organisations already invested in OPA and Rego elsewhere, or that need to enforce the same policy logic across Kubernetes and non-Kubernetes systems (APIs, CI/CD, Terraform), OPA Gatekeeper remains the stronger fit.
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Choose Kyverno if your team is Kubernetes-native and wants policies as plain YAML with fast onboarding and built-in mutation
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Choose OPA Gatekeeper if you need maximum policy expressiveness or want one policy language reused across multiple platforms, not just Kubernetes
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Consider combining both, some 2026 platform teams use Kyverno for Kubernetes-native validation/mutation and OPA/Rego for complex, cross-platform decision logic, rather than treating the choice as strictly either/or
Whichever policy as code tool you choose, the underlying principle stays the same: governance rules that live as version-controlled, automatically enforced code are dramatically more reliable than rules that depend on a human remembering to check them.
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FAQs
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Q1. What is policy as code in Kubernetes?
Policy as code in Kubernetes means enforcing governance rules, security, compliance, resource limits, as version-controlled code through admission controllers like OPA Gatekeeper or Kyverno.
Q2. What is OPA used for?
OPA (Open Policy Agent) is used to enforce policy across many systems, Kubernetes, microservices, CI/CD pipelines, and APIs, using its Rego policy language.
Q3. What is Kyverno used for?
Kyverno is used to validate, mutate, and generate Kubernetes resources through YAML-based policies, purpose-built for Kubernetes without requiring a new policy language.
Q4. What is the difference between OPA Gatekeeper and open policy agent itself?
Open policy agent is the general-purpose policy engine; OPA Gatekeeper is the specific Kubernetes admission webhook that adapts OPA and Rego for enforcing policy inside a Kubernetes cluster.
Q5. Should I choose Kyverno or opa gatekeeper for my cluster?
Choose Kyverno for simpler YAML-based policies and native mutation support; choose opa gatekeeper if you need Rego's expressiveness or want to reuse policy logic beyond Kubernetes.
Q6. Is a kubernetes controller the same thing as an admission webhook?
Not exactly, a kubernetes controller generally reconciles cluster state toward a desired state, while an admission webhook (used by both OPA Gatekeeper and Kyverno) intercepts and evaluates requests before they're persisted.
