add hang_till_terminated

Signed-off-by: wangli <wangli858794774@gmail.com>

Author: Potabk

tests/e2e/conftest.py

@@ -189,7 +189,12 @@ def _poll(self) -> Optional[int]:
         return self.proc.poll()
 
     def hang_until_terminated(self) -> None:
-        """Wait until the server process terminates."""
+        """
+        Wait until the server process terminates.
+        This is for headless mode, where the api server
+        process only exits in the leader node.
+        """
+        pass
 
     def _wait_for_server(self, *, url: str, timeout: float):
         # run health check

tests/e2e/multi_node/config/multi_node_config.py

@@ -72,6 +72,7 @@ def init_dp_param(
     ) -> None:
         self.data_parallel_address = get_net_interface()[0]
         if not is_disaggregate_prefill and not is_leader:
+            # For multi node dp, the workers connect to the leader server.
             self.headless = True
             self.data_parallel_start_rank = dp_size // world_size
             self.data_parallel_address = get_leader_ip()