Admission gate for a rename: RenameGate in flow/rename.py, installed by main.AdmissionGate inside CORS, turns mutating API requests away with 503 renaming and Retry-After while closed and drains those admitted without a limit, abortable; affected flows' hooks get 503 or socket close 1013, reads, sign-in, assistant, workers, artifacts and rename routes pass; the run cache misses while the gate is closed; trigger_node lets EngineHeld through instead of reporting a node failure

backend/fluksio/flow/controller.py

@@ -65,6 +65,7 @@ from fluksio.flow.nodes import (
     WrenNode,
 )
 from fluksio.flow.pipeline import (
+    EngineHeld,
     NodeOutcome,
     Pipeline,
     RunCacheLookup,
@@ -1984,6 +1985,9 @@ class FlowController:
         Returns what the node raised, or an empty string. A node failing by hand
         is reported the way a queued run reports it — on the canvas and in the
         metrics — rather than as a stack trace in the server log.
+
+        :raises EngineHeld: While a rename holds the engine, which is no
+            failure of the node's.
         """
         node = self.get_node(node_id)
         if node is None:
@@ -1993,6 +1997,8 @@ class FlowController:
                 node.trigger(values, durable=False)
             else:
                 node.inject(values or {}, durable=False)
+        except EngineHeld:
+            raise
         except Exception as exc:
             if self.pipeline is None:
                 raise