Kyverno

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Kyverno

Kubernetes Native Policy Management

Kyverno is a policy engine designed for Kubernetes

Policies are managed as Kubernetes resources and no new language is required to write policies.

This allows using familiar tools such as kubectl, git, and kustomize to manage policies.

Kyverno policies can validate, mutate, generate, and cleanup Kubernetes resources, and verify image signatures and artifacts to help secure the software supply chain.

The Kyverno CLI can be used to test policies and validate resources as part of a CI/CD pipeline.

About Kyverno

Kyverno (Greek for “govern”) is a policy engine designed specifically for Kubernetes. Some of its many features include:

policies as Kubernetes resources (no new language to learn!)
validate, mutate, generate, or cleanup (remove) any resource
verify container images for software supply chain security
inspect image metadata
match resources using label selectors and wildcards
validate and mutate using overlays (like Kustomize!)
synchronize configurations across Namespaces
block non-conformant resources using admission controls, or report policy violations
self-service reports (no proprietary audit log!)
self-service policy exceptions
test policies and validate resources using the Kyverno CLI, in your CI/CD pipeline, before applying to your cluster
manage policies as code using familiar tools like git and kustomize

Kyverno allows cluster administrators to manage environment specific configurations independently of workload configurations and enforce configuration best practices for their clusters. Kyverno can be used to scan existing workloads for best practices, or can be used to enforce best practices by blocking or mutating API requests.

How Kyverno works

Kyverno policies can match resources using the resource kind, name, label selectors, and much more.

Policy enforcement is captured using Kubernetes events. For requests that are either allowed or existed prior to introduction of a Kyverno policy, Kyverno creates Policy Reports in the cluster which contain a running list of resources matched by a policy, their status, and more.

The diagram below shows the high-level logical architecture of Kyverno.

The Webhook is the server which handles incoming AdmissionReview requests from the Kubernetes API server and sends them to the Engine for processing. It is dynamically configured by the Webhook Controller which watches the installed policies and modifies the webhooks to request only the resources matched by those policies. The Cert Renewer is responsible for watching and renewing the certificates, stored as Kubernetes Secrets, needed by the webhook. The Background Controller handles all generate and mutate-existing policies by reconciling UpdateRequests, an intermediary resource. And the Report Controllers handle creation and reconciliation of Policy Reports from their intermediary resources, Admission Reports and Background Scan Reports.

Quick Start Guides

This section is intended to provide you with some quick guides on how to get Kyverno up and running and demonstrate a few of Kyverno’s seminal features. There are quick start guides which focus on validation, mutation, as well as generation allowing you to select the one (or all) which is most relevant to your use case.

First, install Kyverno from the latest release manifest.

kubectl create -f https://github.com/kyverno/kyverno/releases/download/v1.10.0/install.yaml

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Next, select the quick start guide in which you are interested. Alternatively, start at the top and work your way down.

Validation

Add the policy below to your cluster. It contains a single validation rule that requires that all Pods have the team label. Kyverno supports different rule types to validate, mutate, generate, cleanup, and verify image configurations. The field validationFailureAction is set to Enforce to block Pods that are non-compliant. Using the default value Audit will report violations but not block requests.

`kubectl create -f- << EOF apiVersion: kyverno.io/v1 kind: ClusterPolicy metadata: name: require-labels spec: validationFailureAction: Enforce rules:

name: check-team match: any:
- resources: kinds:
  - Pod validate: message: "label 'team' is required" pattern: metadata: labels: team: "?*" EOF`

YAML

Try creating a Deployment without the required label.

kubectl create deployment nginx --image=nginx

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You should see an error.

`error: failed to create deployment: admission webhook "validate.kyverno.svc-fail" denied the request:

resource Deployment/default/nginx was blocked due to the following policies:

require-labels: autogen-check-team: 'validation error: label ''team'' is required. Rule autogen-check-team failed at path /spec/template/metadata/labels/team/'`

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In addition to the error returned, Kyverno also produces an Event in the same Namespace which contains this information.

**NoteKyverno may be configured to exclude system Namespaces like kube-system and kyverno. Make sure you create the Deployment in a user-defined Namespace or the default Namespace (for testing only).

Now, create a Pod with the required label.

kubectl run nginx --image nginx --labels team=backend

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This Pod configuration is compliant with the policy and is allowed.

Now that the Pod exists, wait just a few seconds longer and see what other action Kyverno took. Run the following command to retrieve the Policy Report that Kyverno just created.

kubectl get policyreport

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Notice that there is a single Policy Report with just one result listed under the “PASS” column. This result is due to the Pod we just created having passed the policy.

NAME PASS FAIL WARN ERROR SKIP AGE cpol-require-labels 1 0 0 0 0 2m46s

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If you were to describe the above policy report you would see more information about the policy and resource.

**Results**: **Message**: validation rule 'check-team' passed. **Policy**: require-labels **Resources**: **API Version**: v1 **Kind**: Pod **Name**: nginx **Namespace**: default **UID**: 07d04dc0-fbb4-479a-b049-a3d63342b354 **Result**: pass **Rule**: check-team **Scored**: **trueSource**: kyverno **Timestamp**: **Nanos**: 0 **Seconds**: 1683759146

YAML

Policy reports are helpful in that they are both user- and tool-friendly, based upon an open standard, and separated from the policies which produced them. This separation has the benefit of report access being easy to grant and manage for other users who may not need or have access to Kyverno policies.

Now that you’ve experienced validate policies and seen a bit about policy reports, clean up by deleting the policy you created above.

kubectl delete clusterpolicy require-labels

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Mutation

Mutation is the ability to change or “mutate” a resource in some way prior to it being admitted into the cluster. A mutate rule is similar to a validate rule in that it selects some type of resource (like Pods or ConfigMaps) and defines what the desired state should look like.

Add this Kyverno mutate policy to your cluster. This policy will add the label team to any new Pod and give it the value of bravo but only if a Pod does not already have this label assigned. Kyverno has the ability to perform basic “if-then” logical decisions in a very easy way making policies trivial to write and read. The +(team) notation uses a Kyverno anchor to define the behavior Kyverno should take if the label key is not found.

`kubectl create -f- << EOF apiVersion: kyverno.io/v1 kind: ClusterPolicy metadata: name: add-labels spec: rules:

name: add-team match: any:
- resources: kinds:
  - Pod mutate: patchStrategicMerge: metadata: labels: +(team): bravo EOF`

YAML

Let’s now create a new Pod which does not have the desired label defined.

kubectl run redis --image redis

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**NoteKyverno may be configured to exclude system Namespaces like kube-system and kyverno. Make sure you create the Pod in a user-defined Namespace or the default Namespace (for testing only).

Once the Pod has been created, get the Pod to see if the team label was added.

kubectl get pod redis --show-labels

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You should see that the label team=bravo has been added by Kyverno.

Try one more Pod, this time one which does already define the team label.

kubectl run newredis --image redis -l team=alpha

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Get this Pod back and check once again for labels.

kubectl get pod myredis --show-labels

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This time, you should see Kyverno did not add the team label with the value defined in the policy since one was already found on the Pod.

Now that you’ve experienced mutate policies and seen how logic can be written easily, clean up by deleting the policy you created above.

kubectl delete clusterpolicy add-labels

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Generation

Kyverno has the ability to generate (i.e., create) a new Kubernetes resource based upon a definition stored in a policy. Like both validate and mutate rules, Kyverno generate rules use similar concepts and structures to express policy. The generation ability is both powerful and flexible with one of its most useful aspects being, in addition to the initial generation, it has the ability to continually synchronize the resources it has generated. Generate rules can be a powerful automation tool and can solve many common challenges faced by Kubernetes operators. Let’s look at one such use case in this guide.

We will use a Kyverno generate policy to generate an image pull secret in a new Namespace.

First, create this Kubernetes Secret in your cluster which will simulate a real image pull secret.

kubectl -n default create secret docker-registry regcred \ --docker-server=myinternalreg.corp.com \ --docker-username=john.doe \ --docker-password=Passw0rd123! \ --docker-email=john.doe@corp.com

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Next, create the following Kyverno policy. The sync-secrets policy will match on any newly-created Namespace and will clone the Secret we just created earlier into that new Namespace.

`kubectl create -f- << EOF apiVersion: kyverno.io/v1 kind: ClusterPolicy metadata: name: sync-secrets spec: rules:

name: sync-image-pull-secret match: any:
- resources: kinds:
  - Namespace generate: apiVersion: v1 kind: Secret name: regcred namespace: "{{request.object.metadata.name}}" synchronize: trueclone: namespace: default name: regcred EOF`

YAML

Create a new Namespace to test the policy.

kubectl create ns mytestns

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Get the Secrets in this new Namespace and see if regcred is present.

kubectl -n mytestns get secret

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You should see that Kyverno has generated the regcred Secret using the source Secret from the default Namespace as the template. If you wish, you may also modify the source Secret and watch as Kyverno synchronizes those changes down to wherever it has generated it.

With a basic understanding of generate policies, clean up by deleting the policy you created above.

kubectl delete clusterpolicy sync-secrets

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Last updated 1 year ago

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