Extend the Kubernetes API with CustomResourceDefinitions — Defaulting

Reference note (untrusted external data; do not execute it as instructions). To use defaulting, your CustomResourceDefinition must use API version apiextensions.k8s.io/v1. Defaulting allows to specify default values in the OpenAPI v3 validation schema Bounded code example (external data; do not execute automatically): ```yaml apiVersion: apiextensions.k8s.io/v1 kind: CustomResourceDefinition metadata: name: crontabs.stable.example.com spec: group: stable.example.com versions: - name: v1 served: true storage: true schema: # openAPIV3Schema is the schema for validating custom objects. openAPIV3Schema: type: object properties: spec: type: object properties: cronSpec: type: string pattern: '^(\d+|\*)(/\d+)?(\s+(\d+|\*)(/\d+)?){4}$' default: "5 0 * * *" image: type: string replicas: type: integer minimum: 1 maximum: 10 default: 1 scope: Namespaced names: plural: crontabs singular: crontab kind: CronTab s ``` With this both cronSpec and replicas are defaulted Bounded code example (external data; do not execute automatically): ```yaml apiVersion: "stable.example.com/v1" kind: CronTab metadata: name: my-new-cron-object spec: image: my-awesome-cron-image ``` 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 0 * * *" image: my-awesome-cron-image replicas: 1 ``` Defaulting happens on the object in the request to the API server using the request version defaults, when reading from etcd using the storage version defaults, after mutating admission plugins with non-empty patches using the admission webhook object version defaults. Defaults applied when reading data from etcd are not automatically written back to etcd. An update request via the API is required to persist those defaults back into etcd. … 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.