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Kyverno Policy As Code Using CDK8S


  • Kyverno Kyverno is a policy engine designed for Kubernetes, Kyverno policies can validate, mutate, and generate Kubernetes resources plus ensure OCI image supply chain security.
  • In this blog, it provides the way to create Kyverno policy as code using CDK8S typescript.
  • With importing Kyverno CRDs and using CDK8S you can create Kyverno policy manifest using your familiar programming languages such as typescript as scale.

Table Of Contents

๐Ÿš€ Pre-requisite

  • Install typescript, node, and cdk8s as well as projen (optional) which is a tool of managing project configuration as code.
  • Getting started with cdk8s
  • EKS/kubernetes cluster to test

๐Ÿš€ Overview of Kyverno

  • The features are

    • Policies as Kubernetes resources in YAML
    • Validate, mutate, or generate any resource using Kustomize overlays
    • Match resources using label selectors and wildcards
    • Block non-conformant resources using admission controls, or report policy violations
    • Test policies and validate resources using the Kyverno CLI, in your CI/CD pipeline, before applying them to your cluster
  • How does it work?

๐Ÿš€ Import Kyverno CRDs

  • Import kyverno CRDs as cdk8s lib
โšก $ cdk8s import --output src/imports/
Importing resources, this may take a few moments...
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  • Output of importing
    โšก $ tree src/imports/

    0 directories, 1 file
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๐Ÿš€ Write code

  • It's much more convinient to use visual code writing Kyverno policies in typescript language. We can read the document and find all references of construct, objects and properties of Kyverno policies through code descriptions.

  • On top of all polices, there's simple construct (feel free to implement more the construct) so that each policy just need to input name, pattern, etc.

    • Interface of kyverno properties
    export interface KyvernoProps {
      name: string;
      message: string;
      namespace?: string;
      action?: ClusterPolicySpecValidationFailureAction;
      kinds?: Array<string>;
      resources?: {};
      exclude?: ClusterPolicySpecRulesExclude;
      deny?: ClusterPolicySpecRulesValidateDeny;
      pattern?: {};
      anyPatterns?: {};
    • The construct class
    export class KyvernoClusterPolicy extends Chart {
      constructor(scope: Construct, name: string, kyvernoProps: KyvernoProps) {
        super(scope, name);
        new ClusterPolicy(this, `${}`, {
          metadata: {
            namespace: kyvernoProps.namespace || undefined,
            annotations: {
              '': 'Pod Security Standards',
          spec: {
            validationFailureAction: kyvernoProps.action || ClusterPolicySpecValidationFailureAction.ENFORCE,
            rules: [{
              match: {
                any: [{
                  resources: kyvernoProps.resources || { kinds: ['Pod'] },
              validate: {
                deny: kyvernoProps.deny || undefined,
                message: kyvernoProps.message,
                pattern: kyvernoProps.pattern || undefined,
                anyPattern: kyvernoProps.anyPatterns || undefined,
              exclude: kyvernoProps.exclude || undefined,
  • This blog provides example of 5 usecases

    1. Deny delete objects which have label protected: 'true'
    2. require-app-label
    3. require-request-limit
    4. Require run-as-non-root
    5. [Restart Deployment On Configmap Change]

๐Ÿš€ Build Kyverno policy from code

  • Source code:
  โšก $ tree src/
  โ”œโ”€โ”€ imports
  โ”‚   โ””โ”€โ”€
  โ”œโ”€โ”€ kyverno-policies
  โ”‚   โ”œโ”€โ”€ deny-delete-resources.ts
  โ”‚   โ”œโ”€โ”€ kverno-list.ts
  โ”‚   โ”œโ”€โ”€ kyvernoProps.ts
  โ”‚   โ”œโ”€โ”€ require-app-labels.ts
  โ”‚   โ”œโ”€โ”€ require-requests-limits.ts
  โ”‚   โ””โ”€โ”€ require-runasnonroot.ts
  โ”œโ”€โ”€ main.ts
  โ””โ”€โ”€ test-yaml
      โ”œโ”€โ”€ inflate-negative-test-deployment.yaml
      โ””โ”€โ”€ inflate-positive-test-deployment.yaml

  3 directories, 10 files
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  • Build
  โšก $ npx projen build
  ๐Ÿ‘พ build ยป default | ts-node --project .projenrc.ts
  ๐Ÿ‘พ build ยป compile | tsc --build
  ๐Ÿ‘พ build ยป post-compile ยป synth | cdk8s synth
  No manifests synthesized
  ๐Ÿ‘พ build ยป test | jest --passWithNoTests --all --updateSnapshot
  No tests found, exiting with code 0
  File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
  All files |       0 |        0 |       0 |       0 |
  ๐Ÿ‘พ build ยป test ยป eslint | eslint --ext .ts,.tsx --fix --no-error-on-unmatched-pattern src test build-tools projenrc .projenrc.ts
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  • Output yaml files
  โšก $ tree dist/
  โ””โ”€โ”€ kyverno
      โ”œโ”€โ”€ require-app-label-kyverno-policy.yaml
      โ”œโ”€โ”€ require-request-limit-kyverno-policy.yaml
      โ””โ”€โ”€ run-as-non-root-kyverno-policy.yaml

  1 directory, 3 files
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๐Ÿš€ Apply and test

  • Apply policies and check result
  โšก $ kubectl apply -f dist/kyverno/ configured configured configured
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  • Test negative, the deployment inflate-negative-test-deployment.yaml does not have resource limit and request and enable runAsNonRoot
  โšก $ kubectl apply -f src/test-yaml/inflate-negative-test-deployment.yaml
  Error from server: error when creating "src/test-yaml/inflate-negative-test-deployment.yaml": admission webhook "validate.kyverno.svc-fail" denied the request:

  policy Deployment/default/inflate-negative-test for resource violations:

  require-app-label: {}
    autogen-require-request-limit: 'validation error: All containers must have CPU and
      memory resource requests and limits defined. rule autogen-require-request-limit
      failed at path /spec/template/spec/containers/0/resources/limits/'
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  • Test positive
  kubectl apply -f src/test-yaml/inflate-positive-test-deployment.yaml
  deployment.apps/inflate-positive-test created
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  • Test without non-root user enabled, because the validation failure action is AUDIT so the deployment is applied successfully
  โšก $ kubectl apply -f src/test-yaml/inflate-without-nonroot-test-deployment.yaml
  deployment.apps/inflate-without-nonroot-test created
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  • But let's view the policy violations
  โšก $ kubectl describe polr polr-ns-default | grep inflate -A15 -B10| grep "Result: \+fail" -B10
      Seconds:  1661326749
    Category:   Pod Security Standards
    Message:    validation error: Containers must be required to run as non-root users. This policy ensures runAsNonRoot is set to true. rule autogen-run-as-non-root[0] failed at path /spec/template/spec/securityContext/runAsNonRoot/ rule autogen-run-as-non-root[1] failed at path /spec/template/spec/containers/0/securityContext/
    Policy:     run-as-non-root
      API Version:  apps/v1
      Kind:         Deployment
      Name:         inflate-without-nonroot-test
      Namespace:    default
      UID:          b05068c1-425c-41f4-ae0f-c913100a1c9c
    Result:         fail
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๐Ÿš€ Test Restart Deployment On Configmap Change

  • Changing configmap require rollout restart of deployments which reference to that configmap. We can use kyverno to automate this for us.
  • Create kyverno policy to watch a Configmap and if it changes will write an annotation to one or more target Deployments thus triggering a new rollout and thereby refreshing the referred Configmap
  • First we need to grant additional privileges to the Kyverno ServiceAccount for updating apps.deployments resources through Aggregated ClusterRoles

    • Kyverno has clusterrole with aggregationRule which will combine all clusterrole with label app: kyverno into one in aggregation
      - matchLabels:
          app: kyverno
  • Kyverno policy to Restart Deployment On Configmap Change: restart-on-configmap-changes.ts

  • Rebuild project to generate manifest yaml files. npx projen build

  โšก $ tree dist/
  โ”œโ”€โ”€ kyverno
  โ”‚   โ”œโ”€โ”€ require-app-label-kyverno-policy.yaml
  โ”‚   โ”œโ”€โ”€ require-request-limit-kyverno-policy.yaml
  โ”‚   โ”œโ”€โ”€ restart-on-configmap-change-policy.yaml
  โ”‚   โ””โ”€โ”€ run-as-non-root-kyverno-policy.yaml
  โ””โ”€โ”€ role
      โ””โ”€โ”€ kyverno-create-deployments-clusterrole.yaml

  2 directories, 5 files
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  • Apply clusterrole and policy then test using inflate-positive-test-deployment.yaml and inflate-test-configmap.yaml
  โšก $ kv7 get cpol restart-on-configmap-change
  NAME                          BACKGROUND   ACTION    READY
  restart-on-configmap-change   true         audit     true

  โšก $ kv7 get deploy -l app=inflate-positive-test
  NAME                    READY   UP-TO-DATE   AVAILABLE   AGE
  inflate-positive-test   1/1     1            1           62m

  โšก $ kv7 get cm -l app=inflate-test-configmap
  NAME                     DATA   AGE
  inflate-test-configmap   2      64m
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  • We now update the configmap to see kyverno rollout restart the deployment
  โšก $ kv7 apply -f inflate-test-configmap.yaml
  configmap/inflate-test-configmap configured

  ~ $ kv7 get pod -l app=inflate-positive-test --watch
  NAME                                     READY   STATUS    RESTARTS   AGE
  inflate-positive-test-668477b686-cdggl   1/1     Running   0          3m3s
  inflate-positive-test-59bb77549c-lxcjx   0/1     Pending   0          0s
  inflate-positive-test-668477b686-cdggl   1/1     Terminating   0          3m9s
  inflate-positive-test-59bb77549c-lxcjx   0/1     Pending       0          0s
  inflate-positive-test-59bb77549c-lxcjx   0/1     ContainerCreating   0          0s
  inflate-positive-test-59bb77549c-lxcjx   1/1     Running             0          1s
  inflate-positive-test-668477b686-cdggl   1/1     Terminating         0          3m11s
  inflate-positive-test-668477b686-cdggl   1/1     Terminating         0          3m11s
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๐Ÿš€ Conclusion

  • Someone said Kyverno policy as code but the code in yaml language, it's not actual programming language.
  • Using CDK8S to generate Kyverno policy help to leverage the strong programming skill of developer and structure project more efficiently.

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