Kubebuilder: How to force NOT to call Reconcile func again after updating the status subresource?

[angrosz]

Hello,

I'm getting and updating status in my Reconciler code as it is stated on https://book.kubebuilder.io/basics/status_subresource.html page. I noticed that r.Status().Update(context.Background(), instance) triggers new call of Reconcile func. Is it possible NOT to call Reconcile func again after the status subresource is successfully finished?
I need to update the status to READY and finish Reconcile func. Calling again Reconcile func creates the infinitive loop in my code (for PATCH).

Best Regards,
Ania

[jwierzbo]

you can check status value and skip the update if the value is already in the correct state. This will help you avoid the infinity loop.

But yes reconcile after subresource update is frustrating.

[vhosakot]

https://book.kubebuilder.io/basics/status_subresource.html does not exist anymore, use https://book-v1.book.kubebuilder.io/basics/status_subresource.html instead.

[vhosakot]

I see this issue too. Is there a way to skip the Reconcile loop when the status subresource is updated?

I'm following these links:

https://book-v1.book.kubebuilder.io/basics/status_subresource.html

https://book.kubebuilder.io/cronjob-tutorial/controller-implementation.html

Comments below for the reconciled object in cronjob_types.go:

// +k8s:openapi-gen=true
// +kubebuilder:subresource:status
// CronJob is the Schema for the cronjobs API
type CronJob struct {

Comments below for the Reconcile loop in cronjob_controller.go:

// +kubebuilder:rbac:groups=batch.tutorial.kubebuilder.io,resources=cronjobs,verbs=get;list;watch;create;update;patch;delete
// +kubebuilder:rbac:groups=batch.tutorial.kubebuilder.io,resources=cronjobs/status,verbs=get;update;patch
func (r *CronJobReconciler) Reconcile(req ctrl.Request) (ctrl.Result, error) {

status subresource in CRD:

spec:
...
  subresources:
    status: {}
...

Returning reconciler's Result object with Requeue: false set (see below) in the Reconcile loop does not help:

return ctrl.Result{Requeue: false}, r.Status().Update(ctx, &cronJob)

[angrosz]

You can use predicate functions to decide when to skip Reconcile:

p := predicate.Funcs{
    UpdateFunc: func(e event.UpdateEvent) bool {
        oldObject := e.ObjectOld.(*configurationv1.YourCustomResourceDefinition)
        newObject := e.ObjectNew.(*configurationv1.YourCustomResourceDefinition)
        if oldObject.Status != newObject.Status {
            // NO enqueue request
            return false
        }
        // ENQUEUE request
        return true
    },
}

and use this "p" object in Watch function.

// Watch for changes to YourCustomResourceDefinition
err = c.Watch(&source.Kind{Type: &configurationv1.YourCustomResourceDefinition{}}, &handler.EnqueueRequestForObject{}, p)
if err != nil {
    return err
}

I used the following command to generate api:
kubebuilder create api --group configuration --version v1 --kind YourCustomResourceDefinition

Best Regards,
Ania

[vhosakot]

Thanks @angrosz, will try predicate functions and keep you posted.

[DirectXMan12]

the above answer is ok, except that it prevents you from "correcting" changes to status is something else changes status. This is why we generally recommend making controllers idempotent.

[vhosakot]

I was able to use the metadata.generation value in the CR to check if the CR's status was updated and then to decide if the Reconcile loop should be skipped or not.

https://kubernetes.io/docs/tasks/access-kubernetes-api/custom-resources/custom-resource-definitions/#status-subresource says the following about the status subresource:

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

cronjob_types.go:

type CronJobStatus struct {
    // generation (metadata.generation in cronJob CR) observed by the controller
    ObservedGeneration int64 `json:"observedGeneration,omitempty"`
    ...
}

Reconcile loop in cronjob_controller.go:

func (r *CronJobReconciler) Reconcile(req ctrl.Request) (ctrl.Result, error) {
    var cronJob batch.CronJob
    if err := r.Get(ctx, req.NamespacedName, &cronJob); err != nil {
        if cronJob.Status.ObservedGeneration != cronJob.ObjectMeta.Generation {
            Istio.Status.ObservedGeneration = Istio.ObjectMeta.Generation
            r.Status().Update(ctx, &Istio)
            // need to reconcile as cronJob CR is updated
            ...
        } else {
            // cronJob.Status is updated, metadata.generation of
            // cronJob CR is not incremented, no need to reconcile
        }
    }
    ...
}

The above code skips the Reconcile loop when the CR's status subresource is updated.

I see k8s' deployments use the ObservedGeneration field in their status subresource:

$ kubectl get deploy -n=kube-system -o yaml| grep 'status:\|observedGeneration'
  status:
    observedGeneration: 1
  status:
    observedGeneration: 1

https://github.com/kubernetes/api/blob/9b8cae951d65ea28a341b3262d38a058d0935f7c/apps/v1/types.go#L379

[djzager]

Just as a note. You don't necessarily need custom predicate functions. There are a couple in controller-runtime's predicate pkg that may be useful. Specifically, the GenerationChangedPredicate may be what you want.

This is why we generally recommend making controllers idempotent.

This seems like the best advice. One thing that I have found helpful to prevent hotlooping, without using a predicate, is to only update the status once per Reconcile.

[cargaona]

For further reading, using KubeBuilder v2 I managed to use predicates for not reconcile after updating as shown below.

func (r *RedisReconciler) SetupWithManager(mgr ctrl.Manager) error {
    pred := predicate.GenerationChangedPredicate{}
    return ctrl.NewControllerManagedBy(mgr).For(&redisv1beta1.Redis{}).WithEventFilter(pred).Complete(r)
}

All the examples I found were using kubebuilder v1, and the add Add and Watch functions. WithEventFilter is the method you should use to pass the predicate to your controller on the new version.