Provide charm config to set the cinder-csi storage class as the defau…

…lt (#8)

config.yaml

@@ -54,4 +54,12 @@ options:
       through to the parameters.reclaimPolicy field of the csi-cinder-default
       StorageClass.
 
-      Potential values are "Delete" or "Retain"
+      Potential values are "Delete" or "Retain"
+
+  storage-class-default:
+    type: boolean
+    default: false
+    description: |
+      https://kubernetes.io/docs/tasks/administer-cluster/change-default-storage-class/
+      
+      Whether to set the storage class for the Cinder CSI driver as the cluster default

src/storage_manifests.py

@@ -57,12 +57,16 @@ def __call__(self) -> Optional[AnyResource]:
         storage_name = STORAGE_CLASS_NAME.format(type=self.type)
         log.info(f"Creating storage class {storage_name}")
         reclaim_policy: str = self.manifests.config.get("reclaim-policy") or "Delete"
+        is_default: str = "true" if self.manifests.config.get("storage-class-default") else "false"
 
         sc = from_dict(
             dict(
                 apiVersion="storage.k8s.io/v1",
                 kind="StorageClass",
-                metadata=dict(name=storage_name),
+                metadata=dict(
+                    name=storage_name,
+                    annotations={"storageclass.kubernetes.io/is-default-class": is_default},
+                ),
                 provisioner="cinder.csi.openstack.org",
                 reclaimPolicy=reclaim_policy.title(),
                 volumeBindingMode="WaitForFirstConsumer",