Merge pull request #41094 from mrgiles/39212_server_field_validation

Add server side field validation section

Author: k8s-ci-robot

content/en/docs/concepts/overview/working-with-objects/_index.md

@@ -120,6 +120,31 @@ satisfy the StatefulSet specification.
 Different kinds of object can also have different `.status`; again, the API reference pages
 detail the structure of that `.status` field, and its content for each different type of object.
 
+## Server side field validation
+
+Starting with Kubernetes v1.25, the API server offers server side
+[field validation](/docs/reference/using-api/api-concepts/#field-validation)
+that detects unrecognized or duplicate fields in an object. It provides all the functionality
+of `kubectl --validate` on the server side.
+
+The `kubectl` tool uses the `--validate` flag to set the level of field validation. It accepts the
+values `ignore`, `warn`, and `strict` while also accepting the values `true` (equivalent to `strict`)
+and `false` (equivalent to `ignore`). The default validation setting for `kubectl` is `--validate=true`.
+
+`Strict`
+: Strict field validation, errors on validation failure
+
+`Warn`
+: Field validation is performed, but errors are exposed as warnings rather than failing the request
+
+`Ignore`
+: No server side field validation is performed
+
+When `kubectl` cannot connect to an API server that supports field validation it will fall back
+to using client-side validation. Kubernetes 1.27 and later versions always offer field validation;
+older Kubernetes releases might not. If your cluster is older than v1.27, check the documentation
+for your version of Kubernetes.
+
 ## {{% heading "whatsnext" %}}
 
 If you're new to Kubernetes, read more about the following: