Temporarily untarget context when deleting from cell0

When deleting an instance we look it up in the _get_instance
method and if it's in cell0 then the context is permanently
targeted to that cell via the set_target_cell method.

When we delete the instance in _delete we need to temporarily
untarget the context when we decrement the quota usage otherwise
the quota usage gets decremented in the cell0 database rather than
the cell database. Once the instance is deleted then we
re-apply the target cell on the context.

Change-Id: I7de87dce216835729283bca69f0eff59a679b624
Closes-Bug: #1670627

1 files changed, 18 insertions, 10 deletions

diff --git a/nova/context.py b/nova/context.py
index 4dfd025722..be49d2945c 100644
--- a/nova/context.py
+++ b/nova/context.py
@@ -365,17 +365,23 @@ def set_target_cell(context, cell_mapping):
     This is used for permanently targeting a cell in a context.
     Use this when you want all subsequent code to target a cell.
 
+    Passing None for cell_mapping will untarget the context.
+
     :param context: The RequestContext to add connection information
-    :param cell_mapping: An objects.CellMapping object
+    :param cell_mapping: An objects.CellMapping object or None
     """
-    # avoid circular import
-    from nova import db
-    from nova import rpc
-    db_connection_string = cell_mapping.database_connection
-    context.db_connection = db.create_context_manager(db_connection_string)
-    if not cell_mapping.transport_url.startswith('none'):
-        context.mq_connection = rpc.create_transport(
-            cell_mapping.transport_url)
+    if cell_mapping is not None:
+        # avoid circular import
+        from nova import db
+        from nova import rpc
+        db_connection_string = cell_mapping.database_connection
+        context.db_connection = db.create_context_manager(db_connection_string)
+        if not cell_mapping.transport_url.startswith('none'):
+            context.mq_connection = rpc.create_transport(
+                cell_mapping.transport_url)
+    else:
+        context.db_connection = None
+        context.mq_connection = None
 
 
 @contextmanager
@@ -386,8 +392,10 @@ def target_cell(context, cell_mapping):
     This context manager makes a temporary change to the context
     and restores it when complete.
 
+    Passing None for cell_mapping will untarget the context temporarily.
+
     :param context: The RequestContext to add connection information
-    :param cell_mapping: A objects.CellMapping object
+    :param cell_mapping: An objects.CellMapping object or None
     """
     original_db_connection = context.db_connection
     original_mq_connection = context.mq_connection