Handling observedGeneration in status subresource

[G-Goldstein]

Keywords

subresource observedGeneration

Problem

In my update handler for a custom resource, I'd like to set the spec.observedGeneration field to match the latest metadata.generation, as I understand to be good practice.

My CRD defines status as a subresource:

spec:
  group: mycrd.mygroup
  versions:
    - name: v1
      served: true
      storage: true
      subresources:
        status: {}

My understanding is that this means the status subresource can be updated without affecting the metadata.generation value, and I believe #313 introduced the functionality to kopf to support this.

In my handler code, I return observedGeneration on successful completion:

@kopf.on.update('mycrds')
@kopf.on.create('mycrds')
def template_validation(body, name, namespace, **kwargs):
    # Processing omitted for brevity
    return {
      'observedGeneration': body.metadata.get('generation'),
      'valid': 'true',
      'error': None
    }

However, there must be another update happening here because I always find that metadata.generation is 1 higher than status.observedGeneration. In fact, every update to my resource increments metadata.generation by 2 and leaves status.observedGeneration 1 lower.

My guess as to what's happening is that the completion of the handler bumps metadata.generation, pushing it beyond the value I'd retrieved for updating status.observedGeneration. But if kopf is correctly using the Status subresource as suggested by #313 then I'd expect the values to match. Am I mistaken about how this should work, or is there something clever I can do to get them to match? I could of course do this:

'observedGeneration': body.metadata.get('generation') + 1,

but it feels messy, and it doesn't get around the fact that my metadata.generation is increasing by 2 (rather than 1) whenever I manually apply an update.