Run reconciliation when annotations are changed on the resource

[rickardb]

Hi!

I have a use-case where I'd like to run reconciliation when the annotation of a resource has changed. One naive approach to do this would be to add a simple onUpdateFilter to to ControllerConfiguration such as:

class ApiUpdateFilter : OnUpdateFilter<Api> {
        override fun accept(newResource: Api, oldResource: Api): Boolean {
            // or more complex logic to only trigger on specific annotations
            return oldResource.metadata.annotations != newResource.metadata.annotations
        }
    }

However this doesn't work if we don't disable generationAwareEventProcessing as changes to metadata doesn't update the generation version, see https://kubernetes.io/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions/#status-subresource

The .metadata.generation value is incremented for all changes, except for changes to .metadata or .status.

With the way our reconciler is implemented it always results in an update and thus the resourceVersion is updated, i.e. if we disable generationAwareEventProcessingwe we end up in an infinite reconciliation loop. One way to fix this would be to reimplement the default onUpdateGenerationAware filter in our customer filter, but then we also need to re-implement the onUpdateFinalizerNeededAndApplied and so on. This seems like the wrong approach.

Do you have some recommendation on how we could run reconciliation on annotation changes without ending up in some infinite loop?

Cheers,
Rickard

[csviri]

Hi @rickardb

With the way our reconciler is implemented, it always results in an update

So usually this is what is avoided, if it is an update that actually does not change the resource it is fine, that would not result in an event.
Could you tell more why is this needed?

[rickardb]

The only changes I can see to the resource is the resourceVersion and status.lastTransitionTime which seems to result in a new reconciliation loop running.

[csviri]

yes, to that is the reason why, it is observedGeneration is used in status, rather than time. To not trigger the reconciliation all the time.

Also maybe you could reconsider changing the annotation, and putting it into spec?

[rickardb]

Right makes sense. We will change to include it in the spec instead of the annotations. Just wanted to make sure I hadn't missed some obvious way to do this. Thanks!