Generate Resources

Create additional resources based on resource creation or updates.

A generate rule can be used to create additional resources when a new resource is created or when the source is updated. This is useful to create supporting resources, such as new RoleBindings or NetworkPolicies for a Namespace.

The generate rule supports match and exclude blocks, like other rules. Hence, the trigger for applying this rule can be the creation of any resource. It is also possible to match or exclude API requests based on subjects, roles, etc.

The generate rule is triggered during the API CREATE operation. To keep resources synchronized across changes, you can use the synchronize property. When synchronize is set to true, the generated resource is kept in-sync with the source resource (which can be defined as part of the policy or may be an existing resource), and generated resources cannot be modified by users. If synchronize is set to false then users can update or delete the generated resource directly.

Note

As of Kyverno 1.3.0, resources generated with synchronize=true may be modified or deleted by other Kubernetes controllers and users with appropriate access permissions, and Kyverno will recreate or update the resource to comply with configured policies.

When using a generate rule, the origin resource can be either an existing resource defined within Kubernetes, or a new resource defined in the rule itself. When the origin resource is a pre-existing resource such as a ConfigMap or Secret, for example, the clone object is used. When the origin resource is a new resource defined within the manifest of the rule, the data object is used. These are mutually exclusive, and only one may be specified in a rule.

Caution

Deleting the policy containing a generate rule with a data object and synchronize=true will cause immediate deletion of the downstream generated resources. Policies containing a clone object are not subject to this behavior.

Kubernetes has many default resource types even before considering CustomResources defined in CustomResourceDefinitions (CRDs). While Kyverno can generate these CustomResources as well, both these as well as certain default Kubernetes resources may require granting additional privileges to the ClusterRole responsible for the generate behavior. To enable Kyverno to generate these other types, see the section on customizing permissions.

Note

When generating a custom resource, it is necessary to set the apiVersion (ex., spec.generate.apiVersion) and kind (ex., spec.generate.kind).

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.

Generate a ConfigMap using inline data

This policy sets the Zookeeper and Kafka connection strings for all namespaces based upon a ConfigMap defined within the rule itself. Notice that this rule has the generate.data object defined in which case the rule will create a new ConfigMap called zk-kafka-address using the data specified in the rule’s manifest.

 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"

Clone a ConfigMap and propagate changes

In this policy, the source of the data is an existing ConfigMap resource named config-template 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.

 1apiVersion: kyverno.io/v1
 2kind: ClusterPolicy
 3metadata:
 4  name: basic-policy
 5spec:
 6  rules:
 7  - name: Clone ConfigMap
 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 of generated resource
23      kind: ConfigMap
24      # apiVersion of the generated resource
25      apiVersion: v1
26      # Name of the generated resource
27      name: default-config
28      # namespace for the generated resource
29      namespace: "{{request.object.metadata.name}}"
30      # propagate changes from the upstream resource
31      synchronize: true
32      clone:
33        namespace: default
34        name: config-template

Cloning Multiple Resources

Kyverno, as of 1.8, 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 ServiceAccount. This is not a Kyverno function 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 ServiceAccount must have a ClusterRoleBinding in place for that same admin role.

Create a new ClusterRoleBinding for the Kyverno ServiceAccount by default called kyverno.

 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
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 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.

Generate a NetworkPolicy

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

Linking resources with ownerReferences

In some cases, a triggering (source) resource and generated (downstream) resource need to share the same lifecycle. 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. While Kyverno will not take care of this task internally, Kubernetes can by setting the ownerReferences field in the generated resource. 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

With Kyverno 1.7, Kyverno supports the generate for existing resources. Generate existing policies are applied 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.

Generate NetworkPolicy in Existing Namespaces

By default, policy will not be applied on existing trigger resource when it is installed. This behavior can be configured via generateExistingOnPolicyUpdate attribute. Only if you set generateExistingOnPolicyUpdate to true, Kyverno will 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  generateExistingOnPolicyUpdate: 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

Generate PodDisruptionBudget for Existing Deployments

Similarly, this Cluster Policy will create a PodDisruptionBudget resource for existing or new deployments.

 1apiVersion: kyverno.io/v1
 2kind: ClusterPolicy
 3metadata:
 4  name: create-default-pdb
 5spec:
 6  generateExistingOnPolicyUpdate: 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}}"

Troubleshooting

To troubleshoot policy application failures, inspect the UpdateRequest Custom Resource to get details.

For example, if the corresponding permission is not granted to Kyverno, you should see this error in the updaterequest.status:

 1$ kubectl get ur -n kyverno
 2NAME       POLICY               RULETYPE   RESOURCEKIND   RESOURCENAME           RESOURCENAMESPACE   STATUS   AGE
 3ur-7gtbx   create-default-pdb   generate   Deployment     nginx-deployment       test                Failed   2s
 4
 5$ kubectl describe ur ur-7gtbx -n kyverno
 6Name:         ur-7gtbx
 7Namespace:    kyverno
 8...
 9
10status:
11  message: 'poddisruptionbudgets.policy is forbidden: User "system:serviceaccount:kyverno:kyverno-service-account"
12            cannot create resource "poddisruptionbudgets" in API group "policy" in the namespace "test"'
13 state: Failed

Generating resources into existing namespaces

This feature has been deprecated in Kyverno 1.7+, refer to this section to 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 into existing resources, namely the Namespace construct. This can be extremely useful when deploying Kyverno to an existing cluster in use where you wish policy to apply retroactively.

Normally, Kyverno does not alter existing objects in any way as a central tenet of its design. However, using this method of controlled roll-out, you may use generate rules to create new objects into existing Namespaces. To do so, follow these steps:

Identify some Kubernetes label or annotation which is not yet defined on any Namespace but can be used to add to existing ones signaling to Kyverno that these Namespaces should be targets for generate rules. The metadata can be anything, but it should be descriptive for this purpose and not in use anywhere else nor use reserved keys such as kubernetes.io or kyverno.io.
Create a ClusterPolicy with a rule containing a match statement which matches on kind Namespace as well as the label or annotation you have set aside. In the sync-secret policy below, it matches on not only Namespaces but a label of mycorp-rollout=true and copies into these Namespaces a Secret called corp-secret stored in the default Namespace.

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

Create the policy as usual.
On an existing Namespace where you wish to have the Secret corp-secret copied into it, label it with mycorp-rollout=true. This step must be completed after the ClusterPolicy exists. If it is labeled before, Kyverno will not see the request.

1$ kubectl label ns prod-bus-app1 mycorp-rollout=true
2
3namespace/prod-bus-app1 labeled

Check the Namespace you just labeled to see if the Secret exists.

1$ kubectl -n prod-bus-app1 get secret
2
3NAME                                               TYPE                                  DATA   AGE
4corp-secret                                        Opaque                                2      10s

Repeat these steps as needed on any additional Namespaces where you wish this ClusterPolicy to apply its generate rule.

If you would like Kyverno to remove the resource it generated into these existing Namespaces, you may unlabel the Namespace.

1$ kubectl label ns prod-bus-app1 mycorp-rollout-

The Secret from the previous example should be removed.

Last modified October 21, 2022 at 10:39 AM PST: Fix/update language around background scans (#661) (aeaf922)