Only recreate subscriptions in Parallels when necessary

[Cali0707]

Problem
Currently, the reconciler for the Parallel resource deletes and creates a new subscription whenever there is a need for a change in a subscription because some fields in subscriptions are immutable. However, many fields are mutable and in those cases we should be doing an Update instead.

Exit Criteria
A unit test showing that the susbcriptions are updated instead of deleted and recreated

Time Estimate (optional):
How many developer-days do you think this may take to resolve? 1

Additional context (optional)
Add any other context about the feature request here.

• A similar fix for the Sequence resource is here: fix: sequence updates subscription where possible, instead of recreating it #7948
• The relevant reconciler code for the Parallel is here:

  eventing/pkg/reconciler/parallel/parallel.go

  Lines 200 to 235 in 3ee2400

  	func (r *Reconciler) reconcileSubscription(ctx context.Context, branchNumber int, expected *messagingv1.Subscription) (*messagingv1.Subscription, error) {
  	sub, err := r.subscriptionLister.Subscriptions(expected.Namespace).Get(expected.Name)
  	// If the resource doesn't exist, we'll create it.
  	if apierrs.IsNotFound(err) {
  	sub = expected
  	logging.FromContext(ctx).Infof("Creating subscription: %+v", sub)
  	newSub, err := r.eventingClientSet.MessagingV1().Subscriptions(sub.Namespace).Create(ctx, sub, metav1.CreateOptions{})
  	if err != nil {
  	// TODO: Send events here, or elsewhere?
  	//r.Recorder.Eventf(p, corev1.EventTypeWarning, subscriptionCreateFailed, "Create Parallel's subscription failed: %v", err)
  	return nil, fmt.Errorf("failed to create Subscription Object for branch: %d : %s", branchNumber, err)
  	}
  	return newSub, nil
  	} else if err != nil {
  	logging.FromContext(ctx).Errorw("Failed to get Subscription", zap.Error(err))
  	// TODO: Send events here, or elsewhere?
  	//r.Recorder.Eventf(p, corev1.EventTypeWarning, subscriptionCreateFailed, "Create Parallels's subscription failed: %v", err)
  	return nil, fmt.Errorf("failed to get Subscription: %s", err)
  	} else if !equality.Semantic.DeepDerivative(expected.Spec, sub.Spec) {
  	// Given that spec.channel is immutable, we cannot just update the subscription. We delete
  	// it instead, and re-create it.
  	err = r.eventingClientSet.MessagingV1().Subscriptions(sub.Namespace).Delete(ctx, sub.Name, metav1.DeleteOptions{})
  	if err != nil {
  	logging.FromContext(ctx).Infow("Cannot delete Subscription", zap.Error(err))
  	return nil, err
  	}
  	newSub, err := r.eventingClientSet.MessagingV1().Subscriptions(sub.Namespace).Create(ctx, expected, metav1.CreateOptions{})
  	if err != nil {
  	logging.FromContext(ctx).Infow("Cannot create Subscription", zap.Error(err))
  	return nil, err
  	}
  	return newSub, nil
  	}
  	return sub, nil
  	}

[Cali0707]

/good-first-issue

[knative-prow]

@Cali0707:
This request has been marked as suitable for new contributors.

Please ensure the request meets the requirements listed here.

If this request no longer meets these requirements, the label can be removed
by commenting with the /remove-good-first-issue command.

In response to this:

/good-first-issue

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[7h3-3mp7y-m4n]

hey, I would like to work on this

[babugeet]

@7h3-3mp7y-m4n : if you are not able to work on it pls let me know
I would like to work on it
/assign

[7h3-3mp7y-m4n]

I was hoping to work on this and I waited for a member to assign me, I was even trying to reach them through Slack to get more info

[babugeet]

@7h3-3mp7y-m4n I will unassing myself
/unassign

[babugeet]

@7h3-3mp7y-m4n : let me know if you want me to take this up