diff --git a/llumnix/llm_engine_manager.py b/llumnix/llm_engine_manager.py
index 7b47728b..d55b4005 100644
--- a/llumnix/llm_engine_manager.py
+++ b/llumnix/llm_engine_manager.py
@@ -346,27 +346,32 @@ def scale_up(self, instance_id: Union[str, Iterable[str]], llumlet_actor_handles
             instance_id = [instance_id,]
         instance_ids = list(instance_id)
 
-        indeed_update = False
         no_pending_instance = (self.pending_rebuild_migration_instances == 0)
+        indeed_update = False
 
-        for idx, ins_id in enumerate(instance_ids):
+        new_instance_ids = []
+        for ins_id in instance_ids:
             if ins_id not in self.instances:
+                new_instance_ids.append(ins_id)
                 indeed_update = True
-                self.instances[ins_id] = llumlet_actor_handles[idx]
-                self.instance_migrating[ins_id] = False
-                if self.log_instance_info:
-                    self.instance_last_logged_empty[ins_id] = False
                 self.pending_rebuild_migration_instances += 1
-        self.global_scheduler.scale_up(instance_ids)
-        self.num_instances = len(self.instances)
 
         # When scaling up, we need to rebuild the migration backend. But if initially self.pending_rebuild_migration_instances != 0,
         # a coroutine is already handling the changes in the number of instances in the cluster and it will account for the changes
         # caused by this scale-up (see rebuild_migrate_backend for details). Therefore, we simply return in this case. Specifically,
         # for RPC, the Ray actor handle is used for the migration cache, so there is no need to rebuild the group.
-        if self.engine_manager_args.migration_backend != 'rpc' and indeed_update and no_pending_instance:
+        if self.enable_migration and self.engine_manager_args.migration_backend != 'rpc' \
+            and indeed_update and no_pending_instance:
             asyncio.create_task(self.rebuild_migrate_backend())
 
+        for idx, ins_id in enumerate(new_instance_ids):
+            self.instances[ins_id] = llumlet_actor_handles[idx]
+            self.instance_migrating[ins_id] = False
+            if self.log_instance_info:
+                self.instance_last_logged_empty[ins_id] = False
+        self.global_scheduler.scale_up(new_instance_ids)
+        self.num_instances = len(self.instances)
+
         return self.num_instances
 
     def scale_down(self, instance_id: Union[str, Iterable[str]], rebuild_migrate_backend: bool = True) -> None:
@@ -388,7 +393,7 @@ def scale_down(self, instance_id: Union[str, Iterable[str]], rebuild_migrate_bac
         self.global_scheduler.scale_down(instance_ids)
         self.num_instances = len(self.instances)
 
-        if self.engine_manager_args.migration_backend != 'rpc':
+        if self.enable_migration and self.engine_manager_args.migration_backend != 'rpc':
             if len(self.instances) == 0:
                 self.pending_rebuild_migration_instances = 0