python: allow to override the UvicornServer's default log config

It is useful to be able to change Uvicorn's log settings, for example
to be able to change the access log's format.

The Uvicorn's Config class provides a "configure_logging" function
that is smart about the log_config parameter - if it is a string,
and not a dictionary, it is interpreted as a file containing
logging directives and that needs to be loaded from disk.
This is very convenient for the KServe use case: one can either use
the default config, hardcoded in a dictionary, or anything
provided as yaml or json file.

This change fixes also the default UvicornServer's config.

Sadly the current Uvicorn implementation doesn't support
changing the access log format, but they suggest to use
asgi-logger:

encode/uvicorn#947 (comment)

It seems the only way forward to allow a decent customization
of a vital sign like the access log.
The main downside is that asgi-logger requires python3.8+,
so to a temporary workaround could be to add the package as extra
in poetry's config and import the AccessLoggerMiddleware only
if the user sets the access log format.

Fixes: kserve#2778
Signed-off-by: Luca Toscano <toscano.luca@gmail.com>

python/kserve/kserve/model_server.py

@@ -55,6 +55,10 @@
                     help="Enable docs url '/docs' to display Swagger UI.")
 parser.add_argument("--enable_latency_logging", default=True, type=lambda x: bool(strtobool(x)),
                     help="Output a log per request with latency metrics.")
+parser.add_argument("--log_config_file", default=None, type=str,
+                    help="File path containing UvicornServer's log config. Needs to be a yaml or json file.")
+parser.add_argument("--access_log_format", default=None, type=str,
+                    help="Format to set for the access log (provided by asgi-logger).")
 
 args, _ = parser.parse_known_args()
 
@@ -76,6 +80,8 @@ class ModelServer:
         enable_grpc (bool): Whether to turn on grpc server. Default: ``True``
         enable_docs_url (bool): Whether to turn on ``/docs`` Swagger UI. Default: ``False``.
         enable_latency_logging (bool): Whether to log latency metric. Default: ``True``.
+        log_config_file (dict): File path containing UvicornServer's log config. Default: ``None``.
+        access_log_format (string): Format to set for the access log (provided by asgi-logger). Default: ``None``
     """
 
     def __init__(self, http_port: int = args.http_port,
@@ -86,7 +92,9 @@ def __init__(self, http_port: int = args.http_port,
                  registered_models: ModelRepository = ModelRepository(),
                  enable_grpc: bool = args.enable_grpc,
                  enable_docs_url: bool = args.enable_docs_url,
-                 enable_latency_logging: bool = args.enable_latency_logging):
+                 enable_latency_logging: bool = args.enable_latency_logging,
+                 log_config_file: str = args.log_config_file,
+                 access_log_format: str = args.access_log_format):
         self.registered_models = registered_models
         self.http_port = http_port
         self.grpc_port = grpc_port
@@ -100,6 +108,8 @@ def __init__(self, http_port: int = args.http_port,
         self.model_repository_extension = ModelRepositoryExtension(
             model_registry=self.registered_models)
         self._grpc_server = GRPCServer(grpc_port, self.dataplane, self.model_repository_extension)
+        self.log_config_file = log_config_file
+        self.access_log_format = access_log_format
 
     def start(self, models: Union[List[Model], Dict[str, Deployment]]) -> None:
         if isinstance(models, list):
@@ -143,7 +153,9 @@ async def serve():
                     sig, lambda s=sig: asyncio.create_task(self.stop(sig=s))
                 )
             self._rest_server = UvicornServer(self.http_port, [serversocket],
-                                              self.dataplane, self.model_repository_extension, self.enable_docs_url)
+                                              self.dataplane, self.model_repository_extension,
+                                              self.enable_docs_url, log_config_file=self.log_config_file,
+                                              access_log_format=self.access_log_format)
             if self.workers == 1:
                 await self._rest_server.run()
             else:
@@ -153,7 +165,8 @@ async def serve():
                 # https://github.com/tiangolo/fastapi/issues/1586
                 multiprocessing.set_start_method('fork')
                 server = UvicornServer(self.http_port, [serversocket],
-                                       self.dataplane, self.model_repository_extension, self.enable_docs_url)
+                                       self.dataplane, self.model_repository_extension,
+                                       self.enable_docs_url, custom_log_config=self.log_config)
                 for _ in range(self.workers):
                     p = Process(target=server.run_sync)
                     p.start()

python/kserve/kserve/protocol/rest/server.py

@@ -126,7 +126,8 @@ def create_application(self) -> FastAPI:
 
 class UvicornServer:
     def __init__(self, http_port: int, sockets: List[socket.socket],
-                 data_plane: DataPlane, model_repository_extension, enable_docs_url):
+                 data_plane: DataPlane, model_repository_extension, enable_docs_url,
+                 log_config_file: str = None, access_log_format: str = None):
         super().__init__()
         self.sockets = sockets
         rest_server = RESTServer(data_plane, model_repository_extension, enable_docs_url)
@@ -136,46 +137,66 @@ def __init__(self, http_port: int, sockets: List[socket.socket],
             client=PrintTimings(),
             metric_namer=StarletteScopeToName(prefix="kserve.io", starlette_app=app)
         )
+        log_config = {
+            "version": 1,
+            "formatters": {
+                "default": {
+                    "()": "uvicorn.logging.DefaultFormatter",
+                    "datefmt": DATE_FMT,
+                    "fmt": "%(asctime)s.%(msecs)03d %(name)s %(levelprefix)s %(message)s",
+                    "use_colors": None,
+                },
+                "access": {
+                    "()": "uvicorn.logging.AccessFormatter",
+                    "datefmt": DATE_FMT,
+                    "fmt": '%(asctime)s.%(msecs)03d %(name)s %(levelprefix)s %(client_addr)s %(process)s - '
+                           '"%(request_line)s" %(status_code)s',
+                    # noqa: E501
+                },
+            },
+            "handlers": {
+                "default": {
+                    "formatter": "default",
+                    "class": "logging.StreamHandler",
+                    "stream": "ext://sys.stderr",
+                },
+                "access": {
+                    "formatter": "access",
+                    "class": "logging.StreamHandler",
+                    "stream": "ext://sys.stdout",
+                },
+            },
+            "loggers": {
+                "uvicorn": {"handlers": ["default"], "level": "INFO"},
+                "uvicorn.error": {"level": "INFO"},
+                "uvicorn.access": {"handlers": ["access"], "level": "INFO", "propagate": False},
+            },
+        }
+
+        # If the log_config value is a string ending up with ".json"
+        # or ".yaml", it is interpreted as file path and the log configuration
+        # is loaded from disk.
+        if log_config_file:
+            log_config = log_config_file
+
         self.cfg = uvicorn.Config(
             app=app,
             host="0.0.0.0",
+            log_config=log_config,
             port=http_port,
-            log_config={
-                "version": 1,
-                "formatters": {
-                    "default": {
-                        "()": "uvicorn.logging.DefaultFormatter",
-                        "datefmt": DATE_FMT,
-                        "fmt": "%(asctime)s.%(msecs)03d %(name)s %(levelprefix)s %(message)s",
-                        "use_colors": None,
-                    },
-                    "access": {
-                        "()": "uvicorn.logging.AccessFormatter",
-                        "datefmt": DATE_FMT,
-                        "fmt": '%(asctime)s.%(msecs)03d %(name)s %(levelprefix)s %(client_addr)s %(process)s - '
-                               '"%(request_line)s" %(status_code)s',
-                        # noqa: E501
-                    },
-                },
-                "rest": {
-                    "default": {
-                        "formatter": "default",
-                        "class": "logging.StreamHandler",
-                        "stream": "ext://sys.stderr",
-                    },
-                    "access": {
-                        "formatter": "access",
-                        "class": "logging.StreamHandler",
-                        "stream": "ext://sys.stdout",
-                    },
-                },
-                "loggers": {
-                    "uvicorn": {"rest": ["default"], "level": "INFO"},
-                    "uvicorn.error": {"level": "INFO"},
-                    "uvicorn.access": {"rest": ["access"], "level": "INFO", "propagate": False},
-                },
-            }
         )
+
+        # More context in https://github.com/encode/uvicorn/pull/947
+        # At the time of writing the ASGI specs are not clear when it comes
+        # to change the access log format, and hence the Uvicorn upstream devs
+        # chose to create a custom middleware for this.
+        # The allowed log format is specified in https://github.com/Kludex/asgi-logger#usage
+        if access_log_format:
+            from asgi_logger import AccessLoggerMiddleware
+            logging.getLogger("uvicorn.access").handlers = []
+            app.add_middleware(
+                AccessLoggerMiddleware, format=access_log_format)
+
         self.server = _NoSignalUvicornServer(config=self.cfg)
 
     def run_sync(self):

python/kserve/pyproject.toml

@@ -61,6 +61,9 @@ azure-storage-file-share = { version = "~12.7.0", optional = true }
 azure-identity = { version = "^1.8.0", optional = true }
 boto3 = { version = "^1.21.0", optional = true }
 
+# Logging dependencies. They can be opted into by apps.
+asgi-logger = { version = "^0.1.0", optional = true, python = ">3.8.0,<3.11" }
+
 [tool.poetry.extras]
 storage = [
     "urllib3",
@@ -71,6 +74,9 @@ storage = [
     "azure-identity",
     "boto3",
 ]
+logging = [
+    "asgi-logger"
+]
 
 [tool.poetry.group.test]
 optional = true