[BugFix] Fix legacy logger propagation leaking unformatted logs to stderr

fastdeploy/__init__.py

@@ -18,6 +18,7 @@
 # This must be done before importing any modules that may use the logger
 import logging
 import os
+import sys
 from contextlib import contextmanager
 
 # Create standard format (without color)
@@ -29,6 +30,15 @@
 _original_getLogger = logging.getLogger
 
 
+class _MaxLevelFilter(logging.Filter):
+    def __init__(self, level):
+        super().__init__()
+        self.level = level
+
+    def filter(self, record):
+        return record.levelno < self.level
+
+
 @contextmanager
 def _intercept_paddle_loggers():
     """Intercept and configure paddle loggers during import."""
@@ -57,9 +67,16 @@ def _configure_logger(name=None):
     logger.setLevel(logging.DEBUG if envs.FD_DEBUG else logging.INFO)
     for handler in logger.handlers[:]:
         logger.removeHandler(handler)
-    handler = logging.StreamHandler()
-    handler.setFormatter(_root_formatter)
-    logger.addHandler(handler)
+    stdout_handler = logging.StreamHandler(sys.stdout)
+    stdout_handler.setLevel(logging.DEBUG)
+    stdout_handler.addFilter(_MaxLevelFilter(logging.ERROR))
+    stdout_handler.setFormatter(_root_formatter)
+    logger.addHandler(stdout_handler)
+
+    stderr_handler = logging.StreamHandler(sys.stderr)
+    stderr_handler.setLevel(logging.ERROR)
+    stderr_handler.setFormatter(_root_formatter)
+    logger.addHandler(stderr_handler)
     logger.propagate = False
     return logger
 

fastdeploy/engine/sched/scheduler_metrics_logger.py

@@ -15,11 +15,13 @@
 """
 
 import logging
+import sys
 import threading
 import time
 from typing import Iterable
 
 from fastdeploy import envs
+from fastdeploy.logger.logger import _LOG_FORMAT
 
 
 class SchedulerMetricsLogger:
@@ -47,12 +49,8 @@ def _get_logger(self) -> logging.Logger:
         if not getattr(logger, "_fd_scheduler_metrics_configured", False):
             logger.setLevel(logging.INFO)
             logger.propagate = False
-            handler = logging.StreamHandler()
-            formatter = logging.Formatter(
-                "[%(asctime)s] [%(process)d] [%(levelname)s] %(message)s",
-                "%Y-%m-%d %H:%M:%S",
-            )
-            handler.setFormatter(formatter)
+            handler = logging.StreamHandler(sys.stdout)
+            handler.setFormatter(logging.Formatter(_LOG_FORMAT))
             logger.addHandler(handler)
             logger._fd_scheduler_metrics_configured = True
         return logger

fastdeploy/entrypoints/openai/api_server.py

@@ -17,6 +17,7 @@
 import json
 import os
 import signal
+import sys
 import threading
 import time
 import traceback
@@ -194,7 +195,7 @@ async def lifespan(app: FastAPI):
         "%(levelname)-8s %(asctime)s %(process)-5s %(filename)s[line:%(lineno)d] %(message)s"
     )
 
-    handler = logging.StreamHandler()
+    handler = logging.StreamHandler(sys.stdout)
     handler.setFormatter(formatter)
     uvicorn_access.addHandler(handler)
     uvicorn_access.propagate = False

fastdeploy/entrypoints/openai/utils.py

@@ -52,28 +52,35 @@
         }
     },
     "handlers": {
+        # INFO/DEBUG logs go to stdout
         "default": {
+            "class": "colorlog.StreamHandler",
+            "stream": "ext://sys.stdout",
+            "formatter": "custom",
+        },
+        # ERROR+ logs go to stderr
+        "error": {
             "class": "colorlog.StreamHandler",
             "stream": "ext://sys.stderr",
+            "level": "ERROR",
             "formatter": "custom",
         },
     },
     "loggers": {
         "uvicorn": {
             "level": "INFO",
-            "handlers": ["default"],
+            "handlers": ["default", "error"],
             "propagate": False,
         },
         "uvicorn.error": {
             "level": "INFO",
-            "handlers": ["default"],
+            "handlers": ["default", "error"],
             "propagate": False,
         },
         "uvicorn.access": {
             "level": "INFO",
             "handlers": ["default"],
             "propagate": False,
-            "formatter": "custom",
         },
     },
 }

fastdeploy/logger/logger.py

@@ -35,6 +35,30 @@
 _LOG_FORMAT = "%(levelname)-8s %(asctime)s %(process)-5s %(filename)s[line:%(lineno)d] %(message)s"
 
 
+class _MaxLevelFilter(logging.Filter):
+    def __init__(self, level):
+        super().__init__()
+        self.level = level
+
+    def filter(self, record):
+        return record.levelno < self.level
+
+
+def _add_console_handlers(logger, formatter=None):
+    stdout_handler = logging.StreamHandler(sys.stdout)
+    stdout_handler.setLevel(logging.DEBUG)
+    stdout_handler.addFilter(_MaxLevelFilter(logging.ERROR))
+    if formatter is not None:
+        stdout_handler.setFormatter(formatter)
+    logger.addHandler(stdout_handler)
+
+    stderr_handler = logging.StreamHandler(sys.stderr)
+    stderr_handler.setLevel(logging.ERROR)
+    if formatter is not None:
+        stderr_handler.setFormatter(formatter)
+    logger.addHandler(stderr_handler)
+
+
 class FastDeployLogger:
     _instance = None
     _initialized = False
@@ -238,16 +262,11 @@ def get_trace_logger(self, name, file_name, without_formater=False, print_to_con
         logger.addHandler(handler)
         logger.addHandler(error_handler)
 
-        # Console handler
+        # Console handlers: route INFO/DEBUG to stdout and ERROR/CRITICAL to stderr
         if print_to_console:
-            console_handler = logging.StreamHandler()
-            if not without_formater:
-                console_handler.setFormatter(formatter)
-            logger.addHandler(console_handler)
-            console_handler.propagate = False
+            _add_console_handlers(logger, None if without_formater else formatter)
 
-        # Set propagate (maintain original logic)
-        # logger.propagate = False
+        logger.propagate = False
 
         return logger
 
@@ -303,16 +322,11 @@ def _get_legacy_logger(self, name, file_name, without_formater=False, print_to_c
         logger.addHandler(handler)
         logger.addHandler(error_handler)
 
-        # Console handler
+        # Console handlers: route INFO/DEBUG to stdout and ERROR/CRITICAL to stderr
         if print_to_console:
-            console_handler = logging.StreamHandler()
-            if not without_formater:
-                console_handler.setFormatter(formatter)
-            logger.addHandler(console_handler)
-            console_handler.propagate = False
+            _add_console_handlers(logger, None if without_formater else formatter)
 
-        # Set propagate (maintain original logic)
-        # logger.propagate = False
+        logger.propagate = False
 
         return logger
 
@@ -331,9 +345,7 @@ def _patched(name=None):
             logger.setLevel(logging.DEBUG if envs.FD_DEBUG else logging.INFO)
             for handler in logger.handlers[:]:
                 logger.removeHandler(handler)
-            stream_handler = logging.StreamHandler()
-            stream_handler.setFormatter(formatter)
-            logger.addHandler(stream_handler)
+            _add_console_handlers(logger, formatter)
             logger.propagate = False
         return logger
 

fastdeploy/logger/setup_logging.py

@@ -181,6 +181,15 @@ def setup_logging(log_dir=None, config_file=None):
     # Ensure log directory exists
     Path(log_dir).mkdir(parents=True, exist_ok=True)
 
+    # Isolate the 'legacy' logger namespace from the root logger so that
+    # legacy.* loggers never propagate to root even before get_trace_logger
+    # has been called. This is scoped to our own namespace and does NOT
+    # affect third-party libraries that rely on root-level lastResort output.
+    legacy_logger = logging.getLogger("legacy")
+    if not legacy_logger.handlers:
+        legacy_logger.addHandler(logging.NullHandler())
+    legacy_logger.propagate = False
+
     # Store log_dir for later use
     setup_logging._log_dir = log_dir
 

tests/logger/test_logger.py

@@ -81,7 +81,10 @@ def test_legacy_logger_creation(self):
     def test_logger_propagate(self):
         """Test log propagation settings"""
         legacy_logger = self.logger._get_legacy_logger("test", "test.log")
-        self.assertTrue(legacy_logger.propagate)
+        self.assertFalse(legacy_logger.propagate)
+        # Also verify get_trace_logger
+        trace_logger = self.logger.get_trace_logger("test_trace", "test_trace.log")
+        self.assertFalse(trace_logger.propagate)
 
     def test_get_trace_logger_basic(self):
         """Test basic functionality of get_trace_logger"""