Gracefully handle charm initialization when storage not attached (#108)

src/charm.py

@@ -19,7 +19,7 @@
 from charms.tempo_k8s.v2.tracing import TracingEndpointRequirer
 from ops.charm import ActionEvent, CharmBase
 from ops.main import main
-from ops.model import ActiveStatus, BlockedStatus, MaintenanceStatus
+from ops.model import ActiveStatus, BlockedStatus, MaintenanceStatus, ModelError
 from ops.pebble import APIError, ChangeError, ExecError
 
 logger = logging.getLogger(__name__)
@@ -90,10 +90,18 @@ def __init__(self, *args):
             # Storage isn't available yet. Since storage becomes available early enough, no need
             # to observe storage-attached and complicate things; simply abort until it is ready.
             return
-        self._git_sync_mount_point = self.model.storages["content-from-git"][0].location
-        self._repo_path = os.path.join(self._git_sync_mount_point, self.SUBDIR)
+
         self._tracing = TracingEndpointRequirer(self, protocols=["otlp_http"])
 
+        try:
+            self._git_sync_mount_point = self.model.storages["content-from-git"][0].location
+        except ModelError:
+            # Storage isn't available yet. This may happen during the startup sequence.
+            # ops.model.ModelError: ERROR invalid value "content-from-git/1" for option -s: getting filesystem attachment info: filesystem attachment "1" on "unit cos-configuration/0" not provisioned
+            return
+
+        self._repo_path = os.path.join(self._git_sync_mount_point, self.SUBDIR)
+
         self.container = self.unit.get_container(self._container_name)
         self.unit.set_ports(self._git_sync_port)