[Frontend] Pass API server count to each process (#23717)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

vllm/entrypoints/cli/serve.py

@@ -135,23 +135,20 @@ def run_headless(args: argparse.Namespace):
 def run_multi_api_server(args: argparse.Namespace):
 
     assert not args.headless
-    num_api_servers = args.api_server_count
+    num_api_servers: int = args.api_server_count
     assert num_api_servers > 0
 
-    orig_mm_processor_cache_gb = args.mm_processor_cache_gb
-
     if num_api_servers > 1:
         setup_multiprocess_prometheus()
 
-        # Not compatible with API server scale-out
-        args.mm_processor_cache_gb = 0
-
     listen_address, sock = setup_server(args)
 
     engine_args = vllm.AsyncEngineArgs.from_cli_args(args)
+    engine_args._api_process_count = num_api_servers
+    engine_args._api_process_rank = -1
+
     usage_context = UsageContext.OPENAI_API_SERVER
     vllm_config = engine_args.create_engine_config(usage_context=usage_context)
-    model_config = vllm_config.model_config
 
     if num_api_servers > 1:
         if not envs.VLLM_USE_V1:
@@ -161,10 +158,6 @@ def run_multi_api_server(args: argparse.Namespace):
             raise ValueError("VLLM_ALLOW_RUNTIME_LORA_UPDATING cannot be used "
                              "with api_server_count > 1")
 
-        if model_config.is_multimodal_model and orig_mm_processor_cache_gb > 0:
-            logger.warning("Multi-modal processor cache is disabled because "
-                           "it is not compatible with `api_server_count > 1`.")
-
     executor_class = Executor.get_class(vllm_config)
     log_stats = not engine_args.disable_log_stats
 
@@ -221,9 +214,10 @@ def run_api_server_worker_proc(listen_address,
                                client_config=None,
                                **uvicorn_kwargs) -> None:
     """Entrypoint for individual API server worker processes."""
+    client_config = client_config or {}
+    server_index = client_config.get("client_index", 0)
 
     # Set process title and add process-specific prefix to stdout and stderr.
-    server_index = client_config.get("client_index", 0) if client_config else 0
     set_process_title("APIServer", str(server_index))
     decorate_logs()