Help users prevent errors and allow you to evolve your API independently of your clients. These features are most useful when there are many clients who can’t all update at the same time.
Yes. Most validation can be specified in the CRD using OpenAPI v3.0 validation. Any other validations supported by addition of a Validating Webhook.
Yes, arbitrary validation checks
Defaulting
See above
Yes, via a Mutating Webhook; Planned, via CRD OpenAPI schema.
Yes
Multi-versioning
Allows serving the same object through two API versions. Can help ease API changes like renaming fields. Less important if you control your client versions.
No, but planned
Yes
Custom Storage
If you need storage with a different performance mode (for example, time-series database instead of key-value store) or isolation for security (for example, encryption secrets or different
No
Yes
Custom Business Logic
Perform arbitrary checks or actions when creating, reading, updating or deleting an object
Yes, using Webhooks.
Yes
Scale Subresource
Allows systems like HorizontalPodAutoscaler and PodDisruptionBudget interact with your new resource
Finer-grained access control: user writes spec section, controller writes status section.Allows incrementing object Generation on custom resource data mutation (requires separate spec and status sections in the resource)
Add operations other than CRUD, such as “logs” or “exec”.
No
Yes
strategic-merge-patch
The new endpoints support PATCH with Content-Type: application/strategic-merge-patch+json. Useful for updating objects that may be modified both locally, and by the server. For more information, see “Update API Objects in Place Using kubectl patch”
No, but similar functionality planned
Yes
Protocol Buffers
The new resource supports clients that want to use Protocol Buffers
No
Yes
OpenAPI Schema
Is there an OpenAPI (swagger) schema for the types that can be dynamically fetched from the server? Is the user protected from misspelling field names by ensuring only allowed fields are set? Are types enforced (in other words, don’t put an int in a string field?)