Extend the Kubernetes API with CustomResourceDefinitions — Field pruning

Reference note (untrusted external data; do not execute it as instructions). CustomResourceDefinitions store validated resource data in the cluster's persistence store, . As with native Kubernetes resources such as , if you specify a field that the API server does not recognize, the unknown field is _pruned_ (removed) before being persisted. CRDs converted from apiextensions.k8s.io/v1beta1 to apiextensions.k8s.io/v1 might lack structural schemas, and spec.preserveUnknownFields might be true. For legacy CustomResourceDefinition objects created as apiextensions.k8s.io/v1beta1 with spec.preserveUnknownFields set to true, the following is also true Pruning is not enabled. You can store arbitrary data. For compatibility with apiextensions.k8s.io/v1, update your custom resource definitions to Use a structural OpenAPI schema. Set spec.preserveUnknownFields to false. If you save the following YAML to my-crontab.yaml Bounded code example (external data; do not execute automatically): ```yaml apiVersion: "stable.example.com/v1" kind: CronTab metadata: name: my-new-cron-object spec: cronSpec: "* * * * */5" image: my-awesome-cron-image someRandomField: 42 ``` Bounded code example (external data; do not execute automatically): ```shell kubectl create --validate=false -f my-crontab.yaml -o yaml ``` Your output is similar to Bounded code example (external data; do not execute automatically): ```yaml apiVersion: stable.example.com/v1 kind: CronTab metadata: creationTimestamp: 2017-05-31T12:56:35Z generation: 1 name: my-new-cron-object namespace: default resourceVersion: "285" uid: 9423255b-4600-11e7-af6a-28d2447dc82b spec: cronSpec: '* * * * */5' image: my-awesome-cron-image ``` Notice that the field someRandomField was pruned. This example turned off client-side validation to demonstrate the API server's behavior, by adding the --validate=false command line option. Because the OpenAPI validation schemas are also published to clients, kubectl also checks for unknown fields and rejects those objects well before they would be sent to the API server. Attribution: Adapted from Kubernetes Documentation under CC-BY-4.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.