[Logging] allow config logging stream (#24336)

Signed-off-by: Shiyan Deng <dsy842974287@meta.com>

vllm/envs.py

@@ -37,6 +37,7 @@ if TYPE_CHECKING:
     VLLM_CONFIGURE_LOGGING: int = 1
     VLLM_LOGGING_LEVEL: str = "INFO"
     VLLM_LOGGING_PREFIX: str = ""
+    VLLM_LOGGING_STREAM: str = "ext://sys.stdout"
     VLLM_LOGGING_CONFIG_PATH: Optional[str] = None
     VLLM_LOGITS_PROCESSOR_THREADS: Optional[int] = None
     VLLM_LOG_STATS_INTERVAL: float = 10.
@@ -435,6 +436,10 @@ environment_variables: dict[str, Callable[[], Any]] = {
     "VLLM_LOGGING_LEVEL":
     lambda: os.getenv("VLLM_LOGGING_LEVEL", "INFO").upper(),
 
+    # this is used for configuring the default logging stream
+    "VLLM_LOGGING_STREAM":
+    lambda: os.getenv("VLLM_LOGGING_STREAM", "ext://sys.stdout"),
+
     # if set, VLLM_LOGGING_PREFIX will be prepended to all log messages
     "VLLM_LOGGING_PREFIX":
     lambda: os.getenv("VLLM_LOGGING_PREFIX", ""),

vllm/logger.py

@@ -20,6 +20,7 @@ VLLM_CONFIGURE_LOGGING = envs.VLLM_CONFIGURE_LOGGING
 VLLM_LOGGING_CONFIG_PATH = envs.VLLM_LOGGING_CONFIG_PATH
 VLLM_LOGGING_LEVEL = envs.VLLM_LOGGING_LEVEL
 VLLM_LOGGING_PREFIX = envs.VLLM_LOGGING_PREFIX
+VLLM_LOGGING_STREAM = envs.VLLM_LOGGING_STREAM
 
 _FORMAT = (f"{VLLM_LOGGING_PREFIX}%(levelname)s %(asctime)s "
            "[%(fileinfo)s:%(lineno)d] %(message)s")
@@ -38,7 +39,7 @@ DEFAULT_LOGGING_CONFIG = {
             "class": "logging.StreamHandler",
             "formatter": "vllm",
             "level": VLLM_LOGGING_LEVEL,
-            "stream": "ext://sys.stdout",
+            "stream": VLLM_LOGGING_STREAM,
         },
     },
     "loggers": {