refactor: Clean up API constants, and explain usage (#588)

**What problem does this PR solve?**:
We have not explained how we use API constants. We also have good
reasons to remove some constants. This PR does the former, and gets us
closer to the latter.

**Which issue(s) this PR fixes**:
Fixes #

**How Has This Been Tested?**:
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api/v1alpha1/addon_types.go

@@ -6,17 +6,52 @@ package v1alpha1
 import (
 	corev1 "k8s.io/api/core/v1"
 	storagev1 "k8s.io/api/storage/v1"
+
+	nutanixv1 "github.com/nutanix-cloud-native/cluster-api-runtime-extensions-nutanix/api/external/github.com/nutanix-cloud-native/cluster-api-provider-nutanix/api/v1beta1"
 )
 
+// All kubebuilder "Enum" build tag values are available in the OpenAPI spec.
+// So that all these values are available to users of the api package, we
+// we define a constant for each of the values.
+//
+// TODO: Generate these constants from the kubebuilder build tags, if possible.
 const (
-	AddonStrategyClusterResourceSet   AddonStrategy = "ClusterResourceSet"
-	AddonStrategyHelmAddon            AddonStrategy = "HelmAddon"
-	VolumeBindingImmediate                          = storagev1.VolumeBindingImmediate
-	VolumeBindingWaitForFirstConsumer               = storagev1.VolumeBindingWaitForFirstConsumer
+	CNIProviderCalico = "Calico"
+	CNIProviderCilium = "Cilium"
+
+	CSIProviderAWSEBS  = "aws-ebs"
+	CSIProviderNutanix = "nutanix"
+
+	VirtualIPProviderKubeVIP = "KubeVIP"
+
+	AddonStrategyClusterResourceSet AddonStrategy = "ClusterResourceSet"
+	AddonStrategyHelmAddon          AddonStrategy = "HelmAddon"
+
+	VolumeBindingImmediate            = storagev1.VolumeBindingImmediate
+	VolumeBindingWaitForFirstConsumer = storagev1.VolumeBindingWaitForFirstConsumer
 
 	VolumeReclaimRecycle = corev1.PersistentVolumeReclaimRecycle
 	VolumeReclaimDelete  = corev1.PersistentVolumeReclaimDelete
 	VolumeReclaimRetain  = corev1.PersistentVolumeReclaimRetain
+
+	NutanixBootTypeLegacy = nutanixv1.NutanixBootTypeLegacy
+	NutanixBootTypeUEFI   = nutanixv1.NutanixBootTypeUEFI
+)
+
+// FIXME: Remove StorageProvisioner from the API. Users do not provide this
+// value; we derive it from the CSI provider.
+type StorageProvisioner string
+
+const (
+	AWSEBSProvisioner  StorageProvisioner = "ebs.csi.aws.com"
+	NutanixProvisioner StorageProvisioner = "csi.nutanix.com"
+)
+
+// FIXME: Remove the CCM providers from the API. Users do not provider this
+// value; we derive it from the cluster infrastructure.
+const (
+	CCMProviderAWS     = "aws"
+	CCMProviderNutanix = "nutanix"
 )
 
 type Addons struct {

api/v1alpha1/clusterconfig_types.go

@@ -13,21 +13,6 @@ import (
 	"github.com/nutanix-cloud-native/cluster-api-runtime-extensions-nutanix/common/pkg/capi/clustertopology/variables"
 )
 
-type StorageProvisioner string
-
-const (
-	CNIProviderCalico                     = "Calico"
-	CNIProviderCilium                     = "Cilium"
-	AWSEBSProvisioner  StorageProvisioner = "ebs.csi.aws.com"
-	NutanixProvisioner StorageProvisioner = "csi.nutanix.com"
-
-	CSIProviderAWSEBS  = "aws-ebs"
-	CSIProviderNutanix = "nutanix"
-
-	CCMProviderAWS     = "aws"
-	CCMProviderNutanix = "nutanix"
-)
-
 var (
 	DefaultDockerCertSANs = []string{
 		"localhost",

api/v1alpha1/common_types.go

@@ -3,12 +3,6 @@
 
 package v1alpha1
 
-const (
-	APIServerPort = 6443
-
-	VirtualIPProviderKubeVIP = "KubeVIP"
-)
-
 // ObjectMeta is metadata that all persisted resources must have, which includes all objects
 // users must create. This is a copy of customizable fields from metav1.ObjectMeta.
 //

pkg/handlers/generic/lifecycle/ccm/handler.go

@@ -114,6 +114,7 @@ func (c *CCMHandler) AfterControlPlaneInitialized(
 		return
 	}
 
+	// There's a 1:1 mapping of infra to CCM provider. We derive the CCM provider from the infra.
 	infraKind := req.Cluster.Spec.InfrastructureRef.Kind
 	log.Info(fmt.Sprintf("finding CCM handler for %s", infraKind))
 	var handler CCMProvider

pkg/handlers/generic/lifecycle/csi/handler.go

@@ -111,6 +111,7 @@ func (c *CSIHandler) AfterControlPlaneInitialized(
 		}
 	}
 
+	// There's a 1:N mapping of infra to CSI providers. The user chooses the provider.
 	for _, provider := range csiProviders.Providers {
 		handler, ok := c.ProviderHandler[provider.Name]
 		if !ok {