Update labels controller to utilize syncer for updates

[MichalFupso]

Description

Update labels controller to utilize syncer updates to sync labels between k8s and calico nodes

Related issues/PRs

Todos

• Tests
• Documentation
• Release note

Release Note

TBD

Reminder for the reviewer

Make sure that this PR has the correct labels and milestone set.

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Every PR needs one release-note-* label.

• release-note-required: This PR has user-facing changes. Most PRs should have this label.
• release-note-not-required: This PR has no user-facing changes.

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• cherry-pick-candidate: This PR should be cherry-picked to an earlier release. For bug fixes only.
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[lucastigera]

The message says 'skipping node sync,' but the code doesn’t seem to implement a mechanism to skip. Is there a return missing? Is the message incorrect, or did I misunderstand the code? hehe

[lucastigera]

Question:
Is this actually a real 'Error'? I mean, does the system detect an error but still allow the code to continue?
Should it be a 'Warning' instead, or should a return be added to stop execution after logging the error?

[lucastigera]

Just a suggestion to exit early, in order to avoid nested conditions.

Suggested change

	if err != nil {
	logrus.WithError(err).Info("Unable to get corresponding k8s node name, skipping")
	} else if kn != "" {
	// Create a mapping from Kubernetes node -> Calico node.
	logrus.Debugf("Mapping k8s node -> calico node. %s -> %s", kn, n.Name)
	c.k8sNodeMapper[kn] = n.Name
	node, err := c.nodeLister.Get(kn)
	if err != nil {
	logrus.WithError(err).WithField("node", kn).Error("Unable to get node")
	}
	if _, ok := c.calicoNodeCache[n.Name]; !ok {
	// If this is new calicoNode trigger sync for corresponding k8s node.
	// As we only sync labels k8s -> calico node, no need to sync when calico node already exists in our cache
	c.calicoNodeCache[n.Name] = n
	if node != nil && c.syncStatus == bapi.InSync {
	// Only trigger the update if the k8s node exists
	c.k8sNodeUpdate <- node
	}
	return
	}
	c.calicoNodeCache[n.Name] = n
	}
	if err != nil {
	logrus.WithError(err).Info("Unable to get corresponding k8s node name, skipping")
	return
	}
	if kn == "" {
	logrus.WithError(err).Info("Corresponding k8s node name is empty, skipping")
	return
	}
	// Create a mapping from Kubernetes node -> Calico node.
	logrus.Debugf("Mapping k8s node -> calico node. %s -> %s", kn, n.Name)
	c.k8sNodeMapper[kn] = n.Name
	node, err := c.nodeLister.Get(kn)
	if err != nil {
	logrus.WithError(err).WithField("node", kn).Error("Unable to get node")
	}
	_, existsCalicoNode := c.calicoNodeCache[n.Name];
	c.calicoNodeCache[n.Name] = n
	if !existsCalicoNode {
	// If this is new calicoNode trigger sync for corresponding k8s node.
	// As we only sync labels k8s -> calico node, no need to sync when calico node already exists in our cache
	if node != nil && c.syncStatus == bapi.InSync {
	// Only trigger the update if the k8s node exists
	c.k8sNodeUpdate <- node
	}
	}