Restore ordering of worker update in _correct_state_internal

distributed/deploy/spec.py

@@ -381,13 +381,16 @@
             if workers:
                 worker_futs = [asyncio.ensure_future(w) for w in workers]
                 await asyncio.wait(worker_futs)
-                self.workers.update(dict(zip(to_open, workers)))
                 for w in workers:
                     w._cluster = weakref.ref(self)
                 # Collect exceptions from failed workers. This must happen after all
                 # *other* workers have finished initialising, so that we can have a
                 # proper teardown.
                 await asyncio.gather(*worker_futs)
+                # And remember the new workers, note this doesn't
+                # handle partial failure since the gather above would
+                # raise in that case. See also #5919.
+                self.workers.update(dict(zip(to_open, workers)))
 
     def _update_worker_status(self, op, msg):
         if op == "remove":

distributed/deploy/tests/test_local.py

@@ -1275,6 +1275,26 @@ def test_localcluster_start_exception(loop):
             pass
 
 
+def test_localcluster_scale_exception(loop):
+    with raises_with_cause(
+        RuntimeError,
+        "Nanny failed to start",
+        RuntimeError,
+        "Worker failed to start",
+        ImportError,
+        "my_nonexistent_library",
+    ):
+        with LocalCluster(
+            n_workers=0,
+            threads_per_worker=1,
+            processes=True,
+            plugins={MyPlugin()},
+            loop=loop,
+        ) as cluster:
+            cluster.scale(1)
+            cluster.sync(cluster._correct_state)
+
+
 def test_localcluster_get_client(loop):
     with LocalCluster(
         n_workers=0, asynchronous=False, dashboard_address=":0", loop=loop