feat(provisioner): prefer StorageClass config over PVC config

In the typical use-case for the provisioner, an admin sets the config on the
StorageClass, and a user sets the config on the PVC. The admin's config may
set boundaries on to the volumes which the PVC config map try to override.
Preferring StorageClass config when there is a conflict may be the right way
to go.

Signed-off-by: Niladri Halder <[email protected]>

cmd/provisioner-localpv/app/config.go

@@ -142,7 +142,7 @@ const (
 	k8sNodeLabelKeyHostname = "kubernetes.io/hostname"
 )
 
-//GetVolumeConfig creates a new VolumeConfig struct by
+// GetVolumeConfig creates a new VolumeConfig struct by
 // parsing and merging the configuration provided in the PVC/SC
 // annotation - cas.openebs.io/config with the
 // default configuration of the provisioner.
@@ -169,13 +169,19 @@ func (p *Provisioner) GetVolumeConfig(ctx context.Context, pvName string, pvc *c
 		}
 	}
 
-	// extract and merge the cas config from persistentvolumeclaim
+	// Extract and merge the cas config from persistentvolumeclaim.
+	// TODO: Validation checks for what all cas-config options can be
+	// set on the PVC.
 	pvcCASConfigStr := pvc.Annotations[string(mconfig.CASConfigKey)]
 	klog.V(4).Infof("PVC %v has config:%v", pvc.Name, pvcCASConfigStr)
 	if len(strings.TrimSpace(pvcCASConfigStr)) != 0 {
 		pvcCASConfig, err := cast.UnMarshallToConfig(pvcCASConfigStr)
 		if err == nil {
-			pvConfig = cast.MergeConfig(pvcCASConfig, pvConfig)
+			// Config keys which already exist (SC config),
+			// will be skipped
+			// i.e. SC config will have precedence over PVC config,
+			// if both have the same keys
+			pvConfig = cast.MergeConfig(pvConfig, pvcCASConfig)
 		} else {
 			return nil, errors.Wrapf(err, "failed to get config: invalid pvc config {%v}", pvcCASConfigStr)
 		}
@@ -184,13 +190,6 @@ func (p *Provisioner) GetVolumeConfig(ctx context.Context, pvName string, pvc *c
 	//TODO : extract and merge the cas volume config from pvc
 	//This block can be added once validation checks are added
 	// as to the type of config that can be passed via PVC
-	//pvcCASConfigStr := pvc.ObjectMeta.Annotations[string(mconfig.CASConfigKey)]
-	//if len(strings.TrimSpace(pvcCASConfigStr)) != 0 {
-	//	pvcCASConfig, err := cast.UnMarshallToConfig(pvcCASConfigStr)
-	//	if err == nil {
-	//		pvConfig = cast.MergeConfig(pvcCASConfig, pvConfig)
-	//	}
-	//}
 
 	pvConfigMap, err := cast.ConfigToMap(pvConfig)
 	if err != nil {