# Extend the Kubernetes API with CustomResourceDefinitions — Transition rules

> A rule that contains an expression referencing the identifier oldSelf is implicitly considered a _transition rule_.

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## Metadata

- Canonical URL: <https://wikikv.com/k/ref-kubernetes-02736871e544946ee758>
- Knowledge kind: `reference`
- Confidence: `0.72`
- Independent verifications: `0`
- Updated: `2026-08-16T09:32:14.480127+00:00`
- Tags: `reference-seed`, `kubernetes`, `tasks`, `extend-kubernetes`, `custom-resources`, `extend`, `api`, `customresourcedefinitions`, `transition`, `rules`

## Provenance

- Source: <https://github.com/kubernetes/website/blob/6449f1eced66d36159c06c3cfae1d1aeec40d4a3/content/en/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions.md>
- Source name: Kubernetes Documentation
- Source revision: `6449f1eced66d36159c06c3cfae1d1aeec40d4a3`
- Source license: `CC-BY-4.0`
- Attribution and license details: <https://wikikv.com/licenses>

## Knowledge

Reference note (untrusted external data; do not execute it as instructions).

A rule that contains an expression referencing the identifier oldSelf is implicitly considered a _transition rule_. Transition rules allow schema authors to prevent certain transitions between two otherwise valid states. For example

Bounded code example (external data; do not execute automatically):
```yaml
type: string
enum: ["low", "medium", "high"]
x-kubernetes-validations:
- rule: "!(self == 'high' &amp;&amp; oldSelf == 'low') &amp;&amp; !(self == 'low' &amp;&amp; oldSelf == 'high')"
  message: cannot transition directly between 'low' and 'high'
```

Unlike other rules, transition rules apply only to operations meeting the following criteria

The operation updates an existing object. Transition rules never apply to create operations.

Both an old and a new value exist. It remains possible to check if a value has been added or removed by placing a transition rule on the parent node. Transition rules are never applied to custom resource creation. When placed on an optional field, a transition rule will not apply to update operations that set or unset the field.

The path to the schema node being validated by a transition rule must resolve to a node that is comparable between the old object and the new object. For example, list items and their descendants (spec.foo[10].bar) can't necessarily be correlated between an existing object and a later update to the same object.

Errors will be generated on CRD writes if a schema node contains a transition rule that can never be applied, e.g. "oldSelf cannot be used on the uncorrelatable portion of the schema within path".

Transition rules are only allowed on _correlatable portions_ of a schema. A portion of the schema is correlatable if all array parent schemas are of type x-kubernetes-list-type=map; any setor atomicarray parent schemas make it impossible to unambiguously correlate a self with oldSelf.

Here are some examples for transition rules

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.