diff --git a/miles/ray/rollout/rollout_manager.py b/miles/ray/rollout/rollout_manager.py
index 1d8b27e07f..d7c1072b3d 100644
--- a/miles/ray/rollout/rollout_manager.py
+++ b/miles/ray/rollout/rollout_manager.py
@@ -10,6 +10,7 @@
 from miles.ray.rollout.rollout_data_conversion import postprocess_rollout_data
 from miles.ray.rollout.rollout_server import RolloutServer, start_rollout_servers
 from miles.ray.rollout.router_manager import start_session_server
+from miles.ray.rollout.server_cell import get_cell_indexer_of_id_map
 from miles.ray.rollout.train_data_conversion import convert_samples_to_train_data, split_train_data_by_dp
 from miles.ray.utils import Lock
 from miles.rollout.base_types import (
@@ -224,6 +225,17 @@ def _get_updatable_server(self) -> RolloutServer | None:
         )
         return updatable[0] if updatable else None
 
+    # -------------------------- external start/stop -----------------------------
+
+    # TODO
+    # async def start_cell(self):
+    #     pass
+
+    async def stop_cell(self, cell_id: int):
+        idx = get_cell_indexer_of_id_map(self.servers)[cell_id]
+        group = self.servers[idx.srv_key].server_groups[idx.group_index]
+        group.stop_engines(engine_indices=idx.engine_indices)
+
     # -------------------------- misc APIs -----------------------------
 
     def get_num_rollout_per_epoch(self):
diff --git a/miles/ray/rollout/server_cell.py b/miles/ray/rollout/server_cell.py
new file mode 100644
index 0000000000..140bf07880
--- /dev/null
+++ b/miles/ray/rollout/server_cell.py
@@ -0,0 +1,28 @@
+from typing import NamedTuple
+
+from miles.ray.rollout.rollout_server import RolloutServer
+
+
+class CellIndexer(NamedTuple):
+    srv_key: str
+    group_index: int
+    engine_indices: list[int]
+
+
+def get_cell_indexer_of_id_map(servers: dict[str, RolloutServer]) -> list[CellIndexer]:
+    result: list[CellIndexer] = []
+    for srv_key in sorted(servers):
+        srv = servers[srv_key]
+        for group_index, group in enumerate(srv.server_groups):
+            assert len(group.all_engines) == len(group.engines) * group.nodes_per_engine
+            for local_index in range(len(group.engines)):
+                result.append(
+                    CellIndexer(
+                        srv_key=srv_key,
+                        group_index=group_index,
+                        engine_indices=list(
+                            range(local_index * group.nodes_per_engine, (local_index + 1) * group.nodes_per_engine)
+                        ),
+                    )
+                )
+    return result