Add add_logger API to AsyncLLM

tests/v1/metrics/test_engine_logger_apis.py

@@ -0,0 +1,29 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+import pytest
+
+from vllm.v1.engine.async_llm import AsyncEngineArgs, AsyncLLM
+from vllm.v1.metrics.loggers import PrometheusStatLogger
+
+
+@pytest.mark.asyncio
+async def test_async_llm_add_logger():
+    # Minimal model config for test
+    model_name = "distilbert/distilgpt2"
+    dtype = "half"
+    engine_args = AsyncEngineArgs(
+        model=model_name,
+        dtype=dtype,
+        disable_log_stats=False,
+        enforce_eager=True,
+    )
+
+    # Force empty list to avoid default loggers
+    engine = AsyncLLM.from_engine_args(engine_args, stat_loggers=[])
+
+    # Add PrometheusStatLogger and verify no exception is raised
+    await engine.add_logger(PrometheusStatLogger)
+
+    # Verify that logger is present in the first DP rank
+    assert len(engine.stat_loggers[0]) == 1
+    assert isinstance(engine.stat_loggers[0][0], PrometheusStatLogger)

vllm/v1/engine/async_llm.py

@@ -608,6 +608,19 @@ async def collective_rpc(self,
         return await self.engine_core.collective_rpc_async(
             method, timeout, args, kwargs)
 
+    async def add_logger(self, logger_factory: StatLoggerFactory) -> None:
+        if not self.log_stats:
+            raise RuntimeError(
+                "Stat logging is disabled. Set `disable_log_stats=False` "
+                "argument to enable.")
+
+        engine_num = self.vllm_config.parallel_config.data_parallel_size
+        if len(self.stat_loggers) == 0:
+            self.stat_loggers = [[] for _ in range(engine_num)]
+
+        for i, logger_list in enumerate(self.stat_loggers):
+            logger_list.append(logger_factory(self.vllm_config, i))
+
     @property
     def is_running(self) -> bool:
         # Is None before the loop is started.