Support for expectations pattern #2750

Activity

1. csviri

   added this to the 5.1 milestone on Apr 2, 2025
2. csviri

   changed the title [-]Integration of expectation[/-] [+]Integration of expectations[/+] on Apr 2, 2025
3. csviri commented on Apr 25, 2025

   

   csviri

   on Apr 25, 2025

   Last edited by csviri

   CollaboratorAuthor

   More actions

   What I could imaging is to have an API that looks something like this:

   UpdateControl reconcile(Primary primary, Context<Primary> context) {
   
   // omit reconcile details
   
     return UpdateControl.expect((context,primary)-> {
        var resources = context.getSecondaryResources(MyResource.class)
        return checkIfResourcesInExpectedState(resources) 
      },Duration.ofSeconds(5))
   
   }

   In other words, that the reconcile could return an expectation with a timeout, and the reconciliation would not be triggered until that expectation predicate is true or it timeouts.

   While this sounds nice, and might provide a benefit for the users, execution, we won't have too much space to optimize it, so in terms of execution, it would have to be done anyway in the executor service thread that we use now for reconciliation. So this can be directly transformed to something like this:

   UpdateControl reconcile(Primary primary, Context<Primary> context) {
     var resources = context.getSecondaryResources(MyResource.class)
      if (!checkIfResourcesInexpectedState(resources)) {
         return UpdateControl.noUpdate()
      } 
   }

   Except the timeout for which user might have to track hat in a ConcurrentHashMap or such.

   It would be a completely different story if this worked as a cross-cutting filter, where all the event source caches are available.

   It would worth to make a prototype, how that would look like, but for that we would need a new abstraction, probably a subset of Context to access secondary resources from the cache and directly event sources in case.
4. csviri commented on Apr 25, 2025

   

   csviri

   on Apr 25, 2025

   Last edited by csviri

   CollaboratorAuthor

   More actions

   cc @xstefank @metacosm @shawkins, maybe something to discuss in the next community meeting.
5. csviri

   modified the milestones: 5.1, 5.2 on May 14, 2025
6. csviri

   self-assigned this

   on Jun 26, 2025
7. csviri

   linked a pull request that will close this issuefeat: expectations #2840on Jun 26, 2025
8. csviri

   changed the title [-]Integration of expectations[/-] [+]Support for expectations pattern[/+] on Jul 8, 2025
9. csviri commented on Jul 8, 2025

   

   csviri

   on Jul 8, 2025

   CollaboratorAuthor

   More actions

   see also: https://kubernetes.slack.com/archives/C02MRBMN00Z/p1751979029540209
10. csviri

    linked a pull request that will close this issuefeat: expectation pattern support #2941on Sep 13, 2025
11. csviri commented on Sep 22, 2025

    

    csviri

    on Sep 22, 2025

    CollaboratorAuthor

    More actions

    @metacosm
    this is also where this would be needed:
    #2893
    So if the primary resource is deleted we cleanup the expectation map, without finalizer/cleaner interface that has to be done on delete event.
12. metacosm commented on Sep 22, 2025

    

    metacosm

    on Sep 22, 2025

    Collaborator

    More actions

    To be honest, I'm not convinced at all by this feature and I'm not certain that this brings any value to the SDK, nor what use cases this addresses that cannot already be addressed or that we need to address.
13. csviri commented on Sep 22, 2025

    

    csviri

    on Sep 22, 2025

    CollaboratorAuthor

    More actions

    @metacosm isn't is clear from thie blogpost: https://ahmet.im/blog/controller-pitfalls/#expectations-pattern linked to the issue.
    we can explain it on community meeting, if that is not clear enough from there. In case pls let me know which part is not clear.
14. csviri commented on Sep 22, 2025

    

    csviri

    on Sep 22, 2025

    CollaboratorAuthor

    More actions

    Added also link sample expectation from Kubernetes, that might help to understand
15. csviri commented on Sep 22, 2025

    

    csviri

    on Sep 22, 2025

    Last edited by csviri

    CollaboratorAuthor

    More actions

    @metacosm @xstefank pls also check the related PR, although it is WIP, and I'm also checking on the specific use cases in the linked operators (especially karpenter since it is a very prominent one) , the challalneg here that is solved for the user is to manage the state for the expectation (thus timeout) and direct the user into right direction.

    In future we might add actually generic expectation implementations.
16. csviri

    closed this as completedon Nov 26, 2025