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Kyverno Policy As Code Using CDK8S

#cloudopz #kyverno #aws #cdk8s

Abstract

  • 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

🚀 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

🚀 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?

🚀 Import Kyverno CRDs

  • Import kyverno CRDs as cdk8s lib 
⚡ $ cdk8s import https://raw.githubusercontent.com/kyverno/kyverno/main/config/crds/kyverno.io_clusterpolicies.yaml --output src/imports/ Importing resources, this may take a few moments... kyverno.io kyverno.io/clusterpolicy
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  • Output of importing 
 ⚡ $ tree src/imports/ src/imports/ └── kyverno.io.ts 0 directories, 1 file
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🚀 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, `${kyvernoProps.name}`, { metadata: { name: kyvernoProps.name, namespace: kyvernoProps.namespace || undefined, annotations: { 'policies.kyverno.io/category': 'Pod Security Standards', }, }, spec: { validationFailureAction: kyvernoProps.action || ClusterPolicySpecValidationFailureAction.ENFORCE, rules: [{ name: kyvernoProps.name, 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]

🚀 Build Kyverno policy from code

  • Source code: 
 ⚡ $ tree src/ src/ ├── imports │ └── kyverno.io.ts ├── kyverno-policies │ ├── deny-delete-resources.ts │ ├── kverno-list.ts │ ├── kyvernoProps.ts │ ├── require-app-labels.ts │ ├── require-requests-limits.ts │ └── require-runasnonroot.ts ├── main.ts └── test-yaml ├── inflate-negative-test-deployment.yaml └── inflate-positive-test-deployment.yaml 3 directories, 10 files
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  • Build 
 ⚡ $ npx projen build 👾 build » default | ts-node --project tsconfig.dev.json .projenrc.ts 👾 build » compile | tsc --build 👾 build » post-compile » synth | cdk8s synth No manifests synthesized 👾 build » 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 | ----------|---------|----------|---------|---------|------------------- 👾 build » test » 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 
 ⚡ $ tree dist/ dist/ └── kyverno ├── require-app-label-kyverno-policy.yaml ├── require-request-limit-kyverno-policy.yaml └── run-as-non-root-kyverno-policy.yaml 1 directory, 3 files
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🚀 Apply and test

  • Apply policies and check result 
 ⚡ $ kubectl apply -f dist/kyverno/ clusterpolicy.kyverno.io/require-app-label configured clusterpolicy.kyverno.io/require-request-limit configured clusterpolicy.kyverno.io/run-as-non-root configured
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  • Test negative, the deployment inflate-negative-test-deployment.yaml does not have resource limit and request and enable runAsNonRoot 
 ⚡ $ 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: {} require-request-limit: 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 
 ⚡ $ 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 
 ⚡ $ 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 Resources: 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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🚀 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 
    aggregationRule: clusterRoleSelectors: - 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

 ⚡ $ tree dist/ dist/ ├── kyverno │ ├── require-app-label-kyverno-policy.yaml │ ├── require-request-limit-kyverno-policy.yaml │ ├── restart-on-configmap-change-policy.yaml │ └── run-as-non-root-kyverno-policy.yaml └── role └── 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 
 ⚡ $ kv7 get cpol restart-on-configmap-change NAME BACKGROUND ACTION READY restart-on-configmap-change true audit true ⚡ $ kv7 get deploy -l app=inflate-positive-test NAME READY UP-TO-DATE AVAILABLE AGE inflate-positive-test 1/1 1 1 62m ⚡ $ 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 
 ⚡ $ 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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🚀 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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🚀 Vu Dao 🚀

🚀 AWSome Devops | AWS Community Builder | AWS SA || ☁️ CloudOpz ☁️

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