Generate Rules

A generate rule can be used to create new Kubernetes resources in response to some other event including things like resource creation, update, or delete, or even by creating or updating a policy itself. This is useful to create supporting resources, such as new RoleBindings or NetworkPolicies for a Namespace or perform other automation tasks that may either require other tools or be scripted.

Some common use cases for generate rules include:

• Namespace provisioner / Namespace-as-a-Service
  • Create resources like a NetworkPolicy, ResourceQuota, and RoleBinding when a new Namespace is created
• Clone and synchronize Secrets and ConfigMaps
  • Copy and then synchronize changes from one or more Secrets or ConfigMaps to Namespaces across the cluster
• Retroactive creation of NetworkPolicies
  • In brownfield clusters, introduce a policy which will install a NetworkPolicy in all applicable Namespaces from a definition stored in a policy
• Custom eventing system
  • Create Kubernetes Events and associate them with any object and have any message based upon an eligible admission review

Generate rules come in two flavors. They can either apply to admission events that occur across the cluster (ex., creation of a new Namespace), or they can apply to preexisting resources in the cluster (ex., an existing Namespace). Those which apply to admission events are considered standard generate rules while those which apply to preexisting resources are known as “generate existing” rules and are covered below.

Generate rules support match and exclude blocks and many of the other common Kyverno policy constructs such as preconditions, context variables, and more.

Kyverno can keep generated resources in sync to prevent tampering by use of a synchronize property. When synchronize is set to true, the generated resource is kept in-sync with the source resource. Synchronization is beneficial in that modifications to the generated resource may be reverted, and changes to the source resource will be propagated. In addition to these effects, synchronization will ensure that the matching resource responsible for the triggering of the generation behavior is watched for changes. Should those changes result in a false match (including deletion), then it will result in the generated resource being removed to ensure the desired state is always maintained. In cases where the generated resource being synchronized must be modified by other controllers in the cluster, Kyverno can optionally use server-side apply when generating the resource through the field spec.useServerSideApply.

When using a generate rule, the source resource can either be an existing resource in the cluster, or a new resource defined in the rule itself. When the source is an existing resource in the cluster such as a ConfigMap or Secret, for example, the clone object is used. See the Clone Source section for more details. When the source is defined directly in the rule, the data object is used. See the Data Source section for more details. These are mutually exclusive and only one may be specified per rule.

Because Kyverno can generate any type of Kubernetes resource, including custom resources, in some cases it may be necessary to grant the Kyverno background controller’s ServiceAccount additional permissions. To enable Kyverno to generate these other types, see the section on customizing permissions. Kyverno will assist you in these situations by validating and informing you if the background controller does not have the level of permissions required at the time the rule or policy is installed.

Data Source

The source of a generated resource may be defined in the Kyverno policy/rule directly. This is useful in that the full contents of the source can be templated making the resource Kyverno generates highly dynamic and variable depending on the circumstances. To do this, define the generate.data object to store the contents of the resource to be created. Variable templating is supported for all fields in the data object. With synchronization enabled, later modification of the contents of that data object will cause Kyverno to update all downstream (generated) resources with the changes.

The following table shows the behavior of deletion and modification events on components of a generate rule with a data source declaration. “Downstream” refers to the generated resource(s). “Trigger” refers to the resource responsible for triggering the generate rule as defined in a combination of match and exclude blocks. Note that when using a data source with sync enabled, deletion of the rule/policy responsible for a resource’s generation will cause immediate deletion of any/all downstream resources.

Data Examples

This policy sets the Zookeeper and Kafka connection strings for all Namespaces based upon a ConfigMap defined within the rule itself.

 1apiVersion: kyverno.io/v1
 2kind: ClusterPolicy
 3metadata:
 4  name: zk-kafka-address
 5spec:
 6  rules:
 7  - name: k-kafka-address
 8    match:
 9      any:
10      - resources:
11          kinds:
12          - Namespace
13    exclude:
14      any:
15      - resources:
16          namespaces:
17          - kube-system
18          - default
19          - kube-public
20          - kyverno
21    generate:
22      synchronize: true
23      apiVersion: v1
24      kind: ConfigMap
25      name: zk-kafka-address
26      # generate the resource in the new namespace
27      namespace: "{{request.object.metadata.name}}"
28      data:
29        kind: ConfigMap
30        metadata:
31          labels:
32            somekey: somevalue
33        data:
34          ZK_ADDRESS: "192.168.10.10:2181,192.168.10.11:2181,192.168.10.12:2181"
35          KAFKA_ADDRESS: "192.168.10.13:9092,192.168.10.14:9092,192.168.10.15:9092"

In this example, new Namespaces will receive a NetworkPolicy that denies all inbound and outbound traffic. Similar to the first example, the generate.data object is used to define, as an overlay pattern, the spec for the NetworkPolicy resource.

 1apiVersion: kyverno.io/v1
 2kind: ClusterPolicy
 3metadata:
 4  name: default
 5spec:
 6  rules:
 7  - name: deny-all-traffic
 8    match:
 9      any:
10      - resources:
11          kinds:
12          - Namespace
13    exclude:
14      any:
15      - resources:
16          namespaces:
17          - kube-system
18          - default
19          - kube-public
20          - kyverno
21    generate:
22      kind: NetworkPolicy
23      apiVersion: networking.k8s.io/v1
24      name: deny-all-traffic
25      namespace: "{{request.object.metadata.name}}"
26      data:  
27        spec:
28          # select all pods in the namespace
29          podSelector: {}
30          policyTypes:
31          - Ingress
32          - Egress

For other examples of generate rules, see the policy library.

Clone Source

When a generate policy should take the source from a resource which already exists in the cluster, a clone object is used instead of a data object. When triggered, the generate policy will clone from the resource name and location defined in the rule to create the new resource. Use of the clone object implies no modification during the path from source to destination and Kyverno is not able to modify its contents (aside from metadata used for processing and tracking).

The following table shows the behavior of deletion and modification events on components of a generate rule with a clone source declaration. “Downstream” refers to the generated resource(s). “Trigger” refers to the resource responsible for triggering the generate rule as defined in a combination of match and exclude blocks. “Source” refers to the clone source. Note that when using a clone source with sync enabled, deletion of the rule/policy responsible for a resource’s generation or deletion of the clone source will NOT cause deletion of any downstream resources. This behavior differs when compared to data declarations.

Clone Examples

In this policy, designed to clone and keep downstream Secrets in-sync with the source, the source of the data is an existing Secret resource named regcred which is stored in the default Namespace. Notice how the generate rule here instead uses the generate.clone object when the origin data exists within Kubernetes. With synchronization enabled, any modifications to the regcred source Secret in the default Namespace will cause all downstream generated resources to be updated.

 1apiVersion: kyverno.io/v1
 2kind: ClusterPolicy
 3metadata:
 4  name: sync-secrets
 5spec:
 6  rules:
 7  - name: sync-image-pull-secret
 8    match:
 9      any:
10      - resources:
11          kinds:
12          - Namespace
13    generate:
14      apiVersion: v1
15      kind: Secret
16      name: regcred
17      namespace: "{{request.object.metadata.name}}"
18      synchronize: true
19      clone:
20        namespace: default
21        name: regcred

For other examples of generate rules, see the policy library.

Cloning Multiple Resources

Kyverno has the ability to clone multiple resources in a single rule definition for use cases where several resources must be cloned from a source Namespace to a destination Namespace. By using the generate.cloneList object, multiple kinds from the same Namespace may be specified. Use of an optional selector can scope down the source of the clones to only those having the matching label(s). The below policy clones Secrets and ConfigMaps from the staging Namespace which carry the label allowedToBeCloned="true".

 1apiVersion: kyverno.io/v1
 2kind: ClusterPolicy
 3metadata:
 4  name: sync-secret-with-multi-clone
 5spec:
 6  rules:
 7  - name: sync-secret
 8    match:
 9      any:
10      - resources:
11          kinds:
12          - Namespace
13    exclude:
14      any:
15      - resources:
16          namespaces:
17          - kube-system
18          - default
19          - kube-public
20          - kyverno
21    generate:
22      namespace: "{{request.object.metadata.name}}"
23      synchronize: true
24      cloneList:
25        namespace: staging
26        kinds:
27          - v1/Secret
28          - v1/ConfigMap
29        selector:
30          matchLabels:
31            allowedToBeCloned: "true"

Generating Bindings

In order for Kyverno to generate a new RoleBinding or ClusterRoleBinding resource, its ServiceAccount must first be bound to the same Role or ClusterRole which you’re attempting to generate. If this is not done, Kubernetes blocks the request because it sees a possible privilege escalation attempt from the Kyverno background controller’s ServiceAccount. This particularity is not specific to Kyverno but rather how Kubernetes RBAC is designed to work.

For example, if you wish to write a generate rule which creates a new RoleBinding resource granting some user the admin role over a new Namespace, the Kyverno background controller’s ServiceAccount must have a ClusterRoleBinding in place for that same admin role.

Create a new ClusterRoleBinding for the Kyverno background controller’s ServiceAccount

 1apiVersion: rbac.authorization.k8s.io/v1
 2kind: ClusterRoleBinding
 3metadata:
 4  name: kyverno:generate-admin
 5roleRef:
 6  apiGroup: rbac.authorization.k8s.io
 7  kind: ClusterRole
 8  name: admin
 9subjects:
10- kind: ServiceAccount
11  name: kyverno-background-controller
12  namespace: kyverno

Now, create a generate rule as you normally would which assigns a test user named steven to the admin ClusterRole for a new Namespace. The built-in ClusterRole named admin in this rule must match the ClusterRole granted to the Kyverno background controller’s ServiceAccount in the previous ClusterRoleBinding.

 1apiVersion: kyverno.io/v1
 2kind: ClusterPolicy
 3metadata:
 4  name: steven-rolebinding
 5spec:
 6  rules:
 7  - name: steven-rolebinding
 8    match:
 9      any:
10      - resources:
11          kinds:
12          - Namespace
13    generate:
14      kind: RoleBinding
15      apiVersion: rbac.authorization.k8s.io/v1
16      name: steven-rolebinding
17      namespace: "{{request.object.metadata.name}}"
18      data:  
19        subjects:
20        - kind: User
21          name: steven
22          apiGroup: rbac.authorization.k8s.io
23        roleRef:
24          kind: ClusterRole
25          name: admin
26          apiGroup: rbac.authorization.k8s.io

When a new Namespace is created, Kyverno will generate a new RoleBinding called steven-rolebinding which grants the user steven the admin ClusterRole over said new Namespace.

Linking trigger with downstream

In some cases, a triggering (source) resource and generated (downstream) resource need to share the same life cycle. That is, when the triggering resource is deleted so too should the generated resource. This is valuable because some resources are only needed in the presence of another, for example a Service of type LoadBalancer necessitating the need for a specific network policy in some CNI plug-ins.

When a generate rule has synchronization enabled (synchronize: true), deletion of the triggering resource will automatically cause deletion of the downstream (generated) resource. In addition to deletion, if the triggering resource is altered in a way such that it no longer matches the definition in the rule, that too will cause removal of the downstream resource. In cases where synchronization needs to be disabled, if the trigger and downstream are both Namespaced resources and in the same Namespace, the ownerReference technique can be used.

It is possible to set the ownerReferences field in the generated resource which, when pointed to the trigger, will cause deletion of the trigger to instruct Kubernetes to garbage collect the downstream. With the below example, when the generated ConfigMap specifies the metadata.ownerReferences[] object and defines the following fields including uid, which references the triggering Service resource, an owner-dependent relationship is formed. Later, if the Service is deleted, the ConfigMap will be as well. See the Kubernetes documentation for more details including an important caveat around the scoping of these references. Specifically, Namespaced resources cannot be the owners of cluster-scoped resources, and cross-namespace references are also disallowed.

 1apiVersion: kyverno.io/v1
 2kind: ClusterPolicy
 3metadata:
 4  name: demo-ownerref
 5spec:
 6  background: false
 7  rules:
 8  - name: demo-ownerref-svc-cm
 9    match:
10      any:
11      - resources:
12          kinds:
13          - Service
14    generate:
15      kind: ConfigMap
16      apiVersion: v1
17      name: "{{request.object.metadata.name}}-gen-cm"
18      namespace: "{{request.namespace}}"
19      synchronize: false
20      data:
21        metadata:
22          ownerReferences:
23          - apiVersion: v1
24            kind: Service
25            name: "{{request.object.metadata.name}}"
26            uid: "{{request.object.metadata.uid}}"
27        data:
28          foo: bar

Generate for Existing resources

Use of a generate rule is common when creating net new resources from the point after which the policy was created. For example, a Kyverno generate policy is created so that all future Namespaces can receive a standard set of Kubernetes resources. However, it is also possible to generate resources based on existing resources. This can be extremely useful especially for Namespaces when deploying Kyverno to an existing cluster where you wish policy to apply retroactively.

Kyverno supports generation for existing resources. Generate existing policies are applied when the policy is created and in the background which creates target resources based on the match statement within the policy. They may also optionally be configured to apply upon updates to the policy itself. By defining the spec.generateExisting set to true, a generate rule will take effect for existing resources which have the same match characteristics.

Note that the benefits of using a “generate existing” rule is only the moment the policy is installed. Once the initial generation effects have been produced, the rule functions like a “standard” generate rule from that point forward. Generate existing rules are therefore primarily useful for one-time use cases when retroactive policy should be applied.

Generate Existing Examples

By default, policy will not be applied to existing trigger resources when it is installed. This behavior can be configured via generateExisting attribute. Only if you set generateExisting to true will Kyverno generate the target resource in existing triggers on policy CREATE and UPDATE events.

In this example policy, which triggers based on the resource kind Namespace a new NetworkPolicy will be generated in all new or existing Namespaces.

 1apiVersion: kyverno.io/v1
 2kind: ClusterPolicy
 3metadata:
 4  name: generate-resources
 5spec:
 6  generateExisting: true
 7  rules:
 8  - name: generate-existing-networkpolicy
 9    match:
10      any:
11      - resources:
12          kinds:
13          - Namespace
14    generate:
15      kind: NetworkPolicy
16      apiVersion: networking.k8s.io/v1
17      name: default-deny
18      namespace: "{{request.object.metadata.name}}"
19      synchronize: true
20      data:
21        metadata:
22          labels:
23            created-by: kyverno
24        spec:
25          podSelector: {}
26          policyTypes:
27          - Ingress
28          - Egress

Similarly, this ClusterPolicy will create a PodDisruptionBudget resource for existing or new Deployments. Note that use of this policy may require granting of additional permissions as explained above. See the documentation here.

 1apiVersion: kyverno.io/v1
 2kind: ClusterPolicy
 3metadata:
 4  name: create-default-pdb
 5spec:
 6  generateExisting: true
 7  rules:
 8  - name: create-default-pdb
 9    match:
10      any:
11      - resources:
12          kinds:
13          - Deployment
14    exclude:
15      resources:
16        namespaces:
17        - local-path-storage
18    generate:
19      apiVersion: policy/v1
20      kind: PodDisruptionBudget
21      name: "{{request.object.metadata.name}}-default-pdb"
22      namespace: "{{request.object.metadata.namespace}}"
23      synchronize: true
24      data:
25        spec:
26          minAvailable: 1
27          selector:
28            matchLabels:
29              "{{request.object.metadata.labels}}"

How It Works

Kyverno will create an intermediate object called a UpdateRequest which is used to queue work items for the final resource generation. To get the details and status of a generated resource, check the details of the UpdateRequest. The following will give the list of UpdateRequests.

1kubectl get updaterequests -A

A UpdateRequest status can have one of four values:

• Completed: the UpdateRequest controller created resources defined in the policy
• Failed: the UpdateRequest controller failed to process the rules
• Pending: the request is yet to be processed or the resource has not been created
• Skip: marked when triggering the generate policy by adding a label/annotation to the existing resource, while the selector is not defined in the policy itself.

Note that Kyverno will retry up to three times to reconcile an UpdateRequest in a Failed status. The UpdateRequest will be garbage collected if it exceeds the retry threshold.

Kyverno processes generate rules in a combination of the admission controller and the background controller. For further details of the internals of how these work and how high availability and scale are handled, refer to the High Availability page.

Troubleshooting

Troubleshooting of problems with generate rules often comes down to only a few things:

1. Policies no longer work after an upgrade when using the scale to zero method. If possible, delete and attempt to reinstall all generate policies after an upgrade to 1.10 so they may be revalidated. Many fields allowed in previous versions of Kyverno are disallowed going forward.
2. An intermediary UpdateRequest failed to be applied. Although Kyverno checks that the necessary permissions are present at the time a policy is created, either this isn’t happening or there is some other reason why the UpdateRequest cannot be reconciled. See the How It Works section above.
3. The intended trigger did not cause a resource to be generated. Check that Kyverno is not excluding the username or group in its ConfigMap, and check that the resource filter is not discarding those requests. See the Configuring Kyverno guide for details on both.