[Misc] Colorize logs (#29017)

Signed-off-by: Nick Hill <nhill@redhat.com>

tests/test_logger.py

@@ -49,10 +49,13 @@ def test_trace_function_call():
     os.remove(path)
 
 
-def test_default_vllm_root_logger_configuration():
+def test_default_vllm_root_logger_configuration(monkeypatch):
     """This test presumes that VLLM_CONFIGURE_LOGGING (default: True) and
     VLLM_LOGGING_CONFIG_PATH (default: None) are not configured and default
     behavior is activated."""
+    monkeypatch.setenv("VLLM_LOGGING_COLOR", "0")
+    _configure_vllm_root_logger()
+
     logger = logging.getLogger("vllm")
     assert logger.level == logging.DEBUG
     assert not logger.propagate
@@ -70,12 +73,13 @@ def test_default_vllm_root_logger_configuration():
     assert formatter.datefmt == _DATE_FORMAT
 
 
-@patch("vllm.logger.VLLM_CONFIGURE_LOGGING", 1)
-@patch("vllm.logger.VLLM_LOGGING_CONFIG_PATH", None)
-def test_descendent_loggers_depend_on_and_propagate_logs_to_root_logger():
+def test_descendent_loggers_depend_on_and_propagate_logs_to_root_logger(monkeypatch):
     """This test presumes that VLLM_CONFIGURE_LOGGING (default: True) and
     VLLM_LOGGING_CONFIG_PATH (default: None) are not configured and default
     behavior is activated."""
+    monkeypatch.setenv("VLLM_CONFIGURE_LOGGING", "1")
+    monkeypatch.delenv("VLLM_LOGGING_CONFIG_PATH", raising=False)
+
     root_logger = logging.getLogger("vllm")
     root_handler = root_logger.handlers[0]
 
@@ -99,49 +103,50 @@ def test_descendent_loggers_depend_on_and_propagate_logs_to_root_logger():
     assert log_record.levelno == logging.INFO
 
 
-@patch("vllm.logger.VLLM_CONFIGURE_LOGGING", 0)
-@patch("vllm.logger.VLLM_LOGGING_CONFIG_PATH", None)
-def test_logger_configuring_can_be_disabled():
+def test_logger_configuring_can_be_disabled(monkeypatch):
     """This test calls _configure_vllm_root_logger again to test custom logging
     config behavior, however mocks are used to ensure no changes in behavior or
     configuration occur."""
+    monkeypatch.setenv("VLLM_CONFIGURE_LOGGING", "0")
+    monkeypatch.delenv("VLLM_LOGGING_CONFIG_PATH", raising=False)
 
     with patch("vllm.logger.dictConfig") as dict_config_mock:
         _configure_vllm_root_logger()
     dict_config_mock.assert_not_called()
 
 
-@patch("vllm.logger.VLLM_CONFIGURE_LOGGING", 1)
-@patch(
-    "vllm.logger.VLLM_LOGGING_CONFIG_PATH",
-    "/if/there/is/a/file/here/then/you/did/this/to/yourself.json",
-)
-def test_an_error_is_raised_when_custom_logging_config_file_does_not_exist():
+def test_an_error_is_raised_when_custom_logging_config_file_does_not_exist(monkeypatch):
     """This test calls _configure_vllm_root_logger again to test custom logging
     config behavior, however it fails before any change in behavior or
     configuration occurs."""
+    monkeypatch.setenv("VLLM_CONFIGURE_LOGGING", "1")
+    monkeypatch.setenv(
+        "VLLM_LOGGING_CONFIG_PATH",
+        "/if/there/is/a/file/here/then/you/did/this/to/yourself.json",
+    )
+
     with pytest.raises(RuntimeError) as ex_info:
         _configure_vllm_root_logger()
     assert ex_info.type == RuntimeError  # noqa: E721
     assert "File does not exist" in str(ex_info)
 
 
-@patch("vllm.logger.VLLM_CONFIGURE_LOGGING", 1)
-def test_an_error_is_raised_when_custom_logging_config_is_invalid_json():
+def test_an_error_is_raised_when_custom_logging_config_is_invalid_json(monkeypatch):
     """This test calls _configure_vllm_root_logger again to test custom logging
     config behavior, however it fails before any change in behavior or
     configuration occurs."""
+    monkeypatch.setenv("VLLM_CONFIGURE_LOGGING", "1")
+
     with NamedTemporaryFile(encoding="utf-8", mode="w") as logging_config_file:
         logging_config_file.write("---\nloggers: []\nversion: 1")
         logging_config_file.flush()
-        with patch("vllm.logger.VLLM_LOGGING_CONFIG_PATH", logging_config_file.name):
+        monkeypatch.setenv("VLLM_LOGGING_CONFIG_PATH", logging_config_file.name)
         with pytest.raises(JSONDecodeError) as ex_info:
             _configure_vllm_root_logger()
         assert ex_info.type == JSONDecodeError
         assert "Expecting value" in str(ex_info)
 
 
-@patch("vllm.logger.VLLM_CONFIGURE_LOGGING", 1)
 @pytest.mark.parametrize(
     "unexpected_config",
     (
@@ -151,26 +156,30 @@ def test_an_error_is_raised_when_custom_logging_config_is_invalid_json():
     ),
 )
 def test_an_error_is_raised_when_custom_logging_config_is_unexpected_json(
+    monkeypatch,
     unexpected_config: Any,
 ):
     """This test calls _configure_vllm_root_logger again to test custom logging
     config behavior, however it fails before any change in behavior or
     configuration occurs."""
+    monkeypatch.setenv("VLLM_CONFIGURE_LOGGING", "1")
+
     with NamedTemporaryFile(encoding="utf-8", mode="w") as logging_config_file:
         logging_config_file.write(json.dumps(unexpected_config))
         logging_config_file.flush()
-        with patch("vllm.logger.VLLM_LOGGING_CONFIG_PATH", logging_config_file.name):
+        monkeypatch.setenv("VLLM_LOGGING_CONFIG_PATH", logging_config_file.name)
         with pytest.raises(ValueError) as ex_info:
             _configure_vllm_root_logger()
         assert ex_info.type == ValueError  # noqa: E721
         assert "Invalid logging config. Expected dict, got" in str(ex_info)
 
 
-@patch("vllm.logger.VLLM_CONFIGURE_LOGGING", 1)
-def test_custom_logging_config_is_parsed_and_used_when_provided():
+def test_custom_logging_config_is_parsed_and_used_when_provided(monkeypatch):
     """This test calls _configure_vllm_root_logger again to test custom logging
     config behavior, however mocks are used to ensure no changes in behavior or
     configuration occur."""
+    monkeypatch.setenv("VLLM_CONFIGURE_LOGGING", "1")
+
     valid_logging_config = {
         "loggers": {
             "vllm.test_logger.logger": {
@@ -183,19 +192,18 @@ def test_custom_logging_config_is_parsed_and_used_when_provided():
     with NamedTemporaryFile(encoding="utf-8", mode="w") as logging_config_file:
         logging_config_file.write(json.dumps(valid_logging_config))
         logging_config_file.flush()
-        with (
-            patch("vllm.logger.VLLM_LOGGING_CONFIG_PATH", logging_config_file.name),
-            patch("vllm.logger.dictConfig") as dict_config_mock,
-        ):
+        monkeypatch.setenv("VLLM_LOGGING_CONFIG_PATH", logging_config_file.name)
+        with patch("vllm.logger.dictConfig") as dict_config_mock:
             _configure_vllm_root_logger()
             dict_config_mock.assert_called_with(valid_logging_config)
 
 
-@patch("vllm.logger.VLLM_CONFIGURE_LOGGING", 0)
-def test_custom_logging_config_causes_an_error_if_configure_logging_is_off():
+def test_custom_logging_config_causes_an_error_if_configure_logging_is_off(monkeypatch):
     """This test calls _configure_vllm_root_logger again to test custom logging
     config behavior, however mocks are used to ensure no changes in behavior or
     configuration occur."""
+    monkeypatch.setenv("VLLM_CONFIGURE_LOGGING", "0")
+
     valid_logging_config = {
         "loggers": {
             "vllm.test_logger.logger": {
@@ -207,7 +215,7 @@ def test_custom_logging_config_causes_an_error_if_configure_logging_is_off():
     with NamedTemporaryFile(encoding="utf-8", mode="w") as logging_config_file:
         logging_config_file.write(json.dumps(valid_logging_config))
         logging_config_file.flush()
-        with patch("vllm.logger.VLLM_LOGGING_CONFIG_PATH", logging_config_file.name):
+        monkeypatch.setenv("VLLM_LOGGING_CONFIG_PATH", logging_config_file.name)
         with pytest.raises(RuntimeError) as ex_info:
             _configure_vllm_root_logger()
         assert ex_info.type is RuntimeError

vllm/envs.py

@@ -42,6 +42,8 @@ if TYPE_CHECKING:
     VLLM_LOGGING_PREFIX: str = ""
     VLLM_LOGGING_STREAM: str = "ext://sys.stdout"
     VLLM_LOGGING_CONFIG_PATH: str | None = None
+    VLLM_LOGGING_COLOR: str = "auto"
+    NO_COLOR: bool = False
     VLLM_LOG_STATS_INTERVAL: float = 10.0
     VLLM_TRACE_FUNCTION: int = 0
     VLLM_ATTENTION_BACKEND: str | None = None
@@ -616,6 +618,11 @@ environment_variables: dict[str, Callable[[], Any]] = {
     "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", ""),
+    # Controls colored logging output. Options: "auto" (default, colors when terminal),
+    # "1" (always use colors), "0" (never use colors)
+    "VLLM_LOGGING_COLOR": lambda: os.getenv("VLLM_LOGGING_COLOR", "auto"),
+    # Standard unix flag for disabling ANSI color codes
+    "NO_COLOR": lambda: os.getenv("NO_COLOR", "0") != "0",
     # If set, vllm will log stats at this interval in seconds
     # If not set, vllm will log stats every 10 seconds.
     "VLLM_LOG_STATS_INTERVAL": lambda: val
@@ -1578,6 +1585,7 @@ def compile_factors() -> dict[str, object]:
         "VLLM_LOGGING_PREFIX",
         "VLLM_LOGGING_STREAM",
         "VLLM_LOGGING_CONFIG_PATH",
+        "VLLM_LOGGING_COLOR",
         "VLLM_LOG_STATS_INTERVAL",
         "VLLM_DEBUG_LOG_API_SERVER_RESPONSE",
         "VLLM_TUNED_CONFIG_FOLDER",
@@ -1608,6 +1616,7 @@ def compile_factors() -> dict[str, object]:
         "VLLM_TEST_FORCE_LOAD_FORMAT",
         "LOCAL_RANK",
         "CUDA_VISIBLE_DEVICES",
+        "NO_COLOR",
     }
 
     from vllm.config.utils import normalize_value

vllm/logger.py

@@ -17,18 +17,25 @@ from typing import Any, Literal, cast
 
 import vllm.envs as envs
 
-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 "
+    f"{envs.VLLM_LOGGING_PREFIX}%(levelname)s %(asctime)s "
     "[%(fileinfo)s:%(lineno)d] %(message)s"
 )
 _DATE_FORMAT = "%m-%d %H:%M:%S"
 
+
+def _use_color() -> bool:
+    if envs.NO_COLOR or envs.VLLM_LOGGING_COLOR == "0":
+        return False
+    if envs.VLLM_LOGGING_COLOR == "1":
+        return True
+    if envs.VLLM_LOGGING_STREAM == "ext://sys.stdout":  # stdout
+        return hasattr(sys.stdout, "isatty") and sys.stdout.isatty()
+    elif envs.VLLM_LOGGING_STREAM == "ext://sys.stderr":  # stderr
+        return hasattr(sys.stderr, "isatty") and sys.stderr.isatty()
+    return False
+
+
 DEFAULT_LOGGING_CONFIG = {
     "formatters": {
         "vllm": {
@@ -36,13 +43,19 @@ DEFAULT_LOGGING_CONFIG = {
             "datefmt": _DATE_FORMAT,
             "format": _FORMAT,
         },
+        "vllm_color": {
+            "class": "vllm.logging_utils.ColoredFormatter",
+            "datefmt": _DATE_FORMAT,
+            "format": _FORMAT,
+        },
     },
     "handlers": {
         "vllm": {
             "class": "logging.StreamHandler",
-            "formatter": "vllm",
-            "level": VLLM_LOGGING_LEVEL,
-            "stream": VLLM_LOGGING_STREAM,
+            # Choose formatter based on color setting.
+            "formatter": "vllm_color" if _use_color() else "vllm",
+            "level": envs.VLLM_LOGGING_LEVEL,
+            "stream": envs.VLLM_LOGGING_STREAM,
         },
     },
     "loggers": {
@@ -144,7 +157,7 @@ _METHODS_TO_PATCH = {
 def _configure_vllm_root_logger() -> None:
     logging_config = dict[str, Any]()
 
-    if not VLLM_CONFIGURE_LOGGING and VLLM_LOGGING_CONFIG_PATH:
+    if not envs.VLLM_CONFIGURE_LOGGING and envs.VLLM_LOGGING_CONFIG_PATH:
         raise RuntimeError(
             "VLLM_CONFIGURE_LOGGING evaluated to false, but "
             "VLLM_LOGGING_CONFIG_PATH was given. VLLM_LOGGING_CONFIG_PATH "
@@ -152,16 +165,22 @@ def _configure_vllm_root_logger() -> None:
             "VLLM_CONFIGURE_LOGGING or unset VLLM_LOGGING_CONFIG_PATH."
         )
 
-    if VLLM_CONFIGURE_LOGGING:
+    if envs.VLLM_CONFIGURE_LOGGING:
         logging_config = DEFAULT_LOGGING_CONFIG
 
-    if VLLM_LOGGING_CONFIG_PATH:
-        if not path.exists(VLLM_LOGGING_CONFIG_PATH):
+        vllm_handler = logging_config["handlers"]["vllm"]
+        # Refresh these values in case env vars have changed.
+        vllm_handler["level"] = envs.VLLM_LOGGING_LEVEL
+        vllm_handler["stream"] = envs.VLLM_LOGGING_STREAM
+        vllm_handler["formatter"] = "vllm_color" if _use_color() else "vllm"
+
+    if envs.VLLM_LOGGING_CONFIG_PATH:
+        if not path.exists(envs.VLLM_LOGGING_CONFIG_PATH):
             raise RuntimeError(
                 "Could not load logging config. File does not exist: %s",
-                VLLM_LOGGING_CONFIG_PATH,
+                envs.VLLM_LOGGING_CONFIG_PATH,
             )
-        with open(VLLM_LOGGING_CONFIG_PATH, encoding="utf-8") as file:
+        with open(envs.VLLM_LOGGING_CONFIG_PATH, encoding="utf-8") as file:
             custom_config = json.loads(file.read())
 
         if not isinstance(custom_config, dict):

vllm/logging_utils/__init__.py

 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
-from vllm.logging_utils.formatter import NewLineFormatter
+from vllm.logging_utils.formatter import ColoredFormatter, NewLineFormatter
 from vllm.logging_utils.lazy import lazy
 from vllm.logging_utils.log_time import logtime
 
 __all__ = [
     "NewLineFormatter",
+    "ColoredFormatter",
     "lazy",
     "logtime",
 ]

vllm/logging_utils/formatter.py

@@ -75,3 +75,53 @@ class NewLineFormatter(logging.Formatter):
             parts = msg.split(record.message)
             msg = msg.replace("\n", "\r\n" + parts[0])
         return msg
+
+
+class ColoredFormatter(NewLineFormatter):
+    """Adds ANSI color codes to log levels for terminal output.
+
+    This formatter adds colors by injecting them into the format string for
+    static elements (timestamp, filename, line number) and modifying the
+    levelname attribute for dynamic color selection.
+    """
+
+    # ANSI color codes
+    COLORS = {
+        "DEBUG": "\033[37m",  # White
+        "INFO": "\033[32m",  # Green
+        "WARNING": "\033[33m",  # Yellow
+        "ERROR": "\033[31m",  # Red
+        "CRITICAL": "\033[35m",  # Magenta
+    }
+    GREY = "\033[90m"  # Grey for timestamp and file info
+    RESET = "\033[0m"
+
+    def __init__(self, fmt, datefmt=None, style="%"):
+        # Inject grey color codes into format string for timestamp and file info
+        if fmt:
+            # Wrap %(asctime)s with grey
+            fmt = fmt.replace("%(asctime)s", f"{self.GREY}%(asctime)s{self.RESET}")
+            # Wrap [%(fileinfo)s:%(lineno)d] with grey
+            fmt = fmt.replace(
+                "[%(fileinfo)s:%(lineno)d]",
+                f"{self.GREY}[%(fileinfo)s:%(lineno)d]{self.RESET}",
+            )
+
+        # Call parent __init__ with potentially modified format string
+        super().__init__(fmt, datefmt, style)
+
+    def format(self, record):
+        # Store original levelname to restore later (in case record is reused)
+        orig_levelname = record.levelname
+
+        # Only modify levelname - it needs dynamic color based on severity
+        if (color_code := self.COLORS.get(record.levelname)) is not None:
+            record.levelname = f"{color_code}{record.levelname}{self.RESET}"
+
+        # Call parent format which will handle everything else
+        msg = super().format(record)
+
+        # Restore original levelname
+        record.levelname = orig_levelname
+
+        return msg

vllm/utils/system_utils.py

@@ -22,7 +22,7 @@ from .platform_utils import cuda_is_initialized, xpu_is_initialized
 
 logger = init_logger(__name__)
 
-CYAN = "\033[1;36m"
+CYAN = "\033[0;36m"
 RESET = "\033[0;0m"
 
 
@@ -142,6 +142,9 @@ def set_process_title(
 
 def _add_prefix(file: TextIO, worker_name: str, pid: int) -> None:
     """Add colored prefix to file output for log decoration."""
+    if envs.NO_COLOR:
+        prefix = f"({worker_name} pid={pid}) "
+    else:
         prefix = f"{CYAN}({worker_name} pid={pid}){RESET} "
     file_write = file.write