Add middlewares and one specific to expose /metrics endpoint for prometheus (#629)

did this in spare time instead of
#591

using https://github.com/trallnag/prometheus-fastapi-instrumentator

these middlewares can be enabled via CLI if referenced by their `type`
ClassVar:
```
$ mlem --tb serve fastapi --model ../emoji/lyrics2emoji --middlewares.0 prometheus_fastapi
```

---------

Co-authored-by: mike0sv <[email protected]>

Author: aguschin

mlem/contrib/fastapi.py

@@ -4,6 +4,7 @@
 FastAPIServer implementation
 """
 import logging
+from abc import ABC, abstractmethod
 from collections.abc import Callable
 from types import ModuleType
 from typing import Any, ClassVar, Dict, List, Optional, Tuple, Type
@@ -24,6 +25,7 @@
     InterfaceArgument,
     InterfaceMethod,
 )
+from mlem.runtime.middleware import Middleware, Middlewares
 from mlem.runtime.server import Server
 from mlem.ui import EMOJI_NAILS, echo
 from mlem.utils.module import get_object_requirements
@@ -48,6 +50,12 @@ def _create_schema_route(app: FastAPI, interface: Interface):
     app.add_api_route("/interface.json", lambda: schema, tags=["schema"])
 
 
+class FastAPIMiddleware(Middleware, ABC):
+    @abstractmethod
+    def on_app_init(self, app: FastAPI):
+        raise NotImplementedError
+
+
 class FastAPIServer(Server, LibRequirementsMixin):
     """Serves model with http"""
 
@@ -70,6 +78,7 @@ def _create_handler_executor(
         arg_serializers: Dict[str, DataTypeSerializer],
         executor: Callable,
         response_serializer: DataTypeSerializer,
+        middlewares: Middlewares,
     ):
         deserialized_model = create_model(
             "Model", **{a: (Any, ...) for a in args}
@@ -99,7 +108,9 @@ def serializer_validator(_, values):
 
             def bin_handler(model: schema_model):  # type: ignore[valid-type]
                 values = {a: getattr(model, a) for a in args}
+                values = middlewares.on_request(values)
                 result = executor(**values)
+                result = middlewares.on_response(values, result)
                 with response_serializer.dump(result) as buffer:
                     return StreamingResponse(
                         buffer, media_type="application/octet-stream"
@@ -113,7 +124,9 @@ def bin_handler(model: schema_model):  # type: ignore[valid-type]
 
         def handler(model: schema_model):  # type: ignore[valid-type]
             values = {a: getattr(model, a) for a in args}
+            values = middlewares.on_request(values)
             result = executor(**values)
+            result = middlewares.on_response(values, result)
             response = response_serializer.serialize(result)
             return parse_obj_as(response_model, response)
 
@@ -127,12 +140,15 @@ def _create_handler_executor_binary(
         arg_name: str,
         executor: Callable,
         response_serializer: DataTypeSerializer,
+        middlewares: Middlewares,
     ):
         if response_serializer.serializer.is_binary:
 
             def bin_handler(file: UploadFile):
                 arg = serializer.deserialize(_SpooledFileIOWrapper(file.file))
+                arg = middlewares.on_request(arg)
                 result = executor(**{arg_name: arg})
+                result = middlewares.on_response(arg, result)
                 with response_serializer.dump(result) as buffer:
                     return StreamingResponse(
                         buffer, media_type="application/octet-stream"
@@ -146,15 +162,20 @@ def bin_handler(file: UploadFile):
 
         def handler(file: UploadFile):
             arg = serializer.deserialize(file.file)
+            arg = middlewares.on_request(arg)
             result = executor(**{arg_name: arg})
-
+            result = middlewares.on_response(arg, result)
             response = response_serializer.serialize(result)
             return parse_obj_as(response_model, response)
 
         return handler, response_model, None
 
     def _create_handler(
-        self, method_name: str, signature: InterfaceMethod, executor: Callable
+        self,
+        method_name: str,
+        signature: InterfaceMethod,
+        executor: Callable,
+        middlewares: Middlewares,
     ) -> Tuple[Optional[Callable], Optional[Type], Optional[Response]]:
         serializers, response_serializer = self._get_serializers(signature)
         echo(EMOJI_NAILS + f"Adding route for /{method_name}")
@@ -170,13 +191,15 @@ def _create_handler(
                 arg_name,
                 executor,
                 response_serializer,
+                middlewares,
             )
         return self._create_handler_executor(
             method_name,
             {a.name: a for a in signature.args},
             serializers,
             executor,
             response_serializer,
+            middlewares,
         )
 
     def app_init(self, interface: Interface):
@@ -185,11 +208,15 @@ def app_init(self, interface: Interface):
         app.add_api_route(
             "/", lambda: RedirectResponse("/docs"), include_in_schema=False
         )
+        for mid in self.middlewares.__root__:
+            mid.on_init()
+            if isinstance(mid, FastAPIMiddleware):
+                mid.on_app_init(app)
 
         for method, signature in interface.iter_methods():
             executor = interface.get_method_executor(method)
             handler, response_model, response_class = self._create_handler(
-                method, signature, executor
+                method, signature, executor, self.middlewares
             )
 
             app.add_api_route(

mlem/contrib/prometheus.py

@@ -0,0 +1,65 @@
+"""Instrumenting FastAPI app to expose metrics for prometheus
+Extension type: middleware
+
+Exposes /metrics endpoint
+"""
+from typing import ClassVar, List, Optional
+
+from fastapi import FastAPI
+from prometheus_fastapi_instrumentator import Instrumentator
+
+from mlem.contrib.fastapi import FastAPIMiddleware
+from mlem.utils.importing import import_string_with_local
+from mlem.utils.module import get_object_requirements
+
+
+class PrometheusFastAPIMiddleware(FastAPIMiddleware):
+    """Middleware for FastAPI server that exposes /metrics endpoint to be scraped by Prometheus"""
+
+    type: ClassVar = "prometheus_fastapi"
+
+    metrics: List[str] = []
+    """Instrumentator instance to use. If not provided, a new one will be created"""
+    instrumentator_cache: Optional[Instrumentator] = None
+
+    class Config:
+        arbitrary_types_allowed = True
+        exclude = {"instrumentator_cache"}
+
+    @property
+    def instrumentator(self):
+        if self.instrumentator_cache is None:
+            self.instrumentator_cache = self.get_instrumentator()
+        return self.instrumentator_cache
+
+    def on_app_init(self, app: FastAPI):
+        @app.on_event("startup")
+        async def _startup():
+            self.instrumentator.expose(app)
+
+    def on_init(self):
+        pass
+
+    def on_request(self, request):
+        return request
+
+    def on_response(self, request, response):
+        return response
+
+    def get_instrumentator(self):
+        instrumentator = Instrumentator()
+        for metric in self._iter_metric_objects():
+            # todo: check object type
+            instrumentator.add(metric)
+        return instrumentator
+
+    def _iter_metric_objects(self):
+        for metric in self.metrics:
+            # todo: meaningful error on import error
+            yield import_string_with_local(metric)
+
+    def get_requirements(self):
+        reqs = super().get_requirements()
+        for metric in self._iter_metric_objects():
+            reqs += get_object_requirements(metric)
+        return reqs

mlem/contrib/sagemaker/runtime.py

@@ -62,6 +62,7 @@ def app_init(self, interface: Interface):
             "invocations",
             interface.get_method_signature(self.method),
             interface.get_method_executor(self.method),
+            self.middlewares,
         )
         app.add_api_route(
             "/invocations",

mlem/core/base.py

@@ -1,5 +1,4 @@
 import shlex
-import sys
 from collections import defaultdict
 from inspect import isabstract
 from typing import (
@@ -22,7 +21,7 @@
 
 from mlem.core.errors import ExtensionRequirementError, UnknownImplementation
 from mlem.polydantic import PolyModel
-from mlem.utils.importing import import_string
+from mlem.utils.importing import import_string_with_local
 from mlem.utils.path import make_posix
 
 
@@ -64,18 +63,12 @@ def load_impl_ext(
 
     if type_name is not None and "." in type_name:
         try:
-            # this is needed because if run from cli curdir is not checked for
-            # modules to import
-            sys.path.append(".")
-
-            obj = import_string(type_name)
+            obj = import_string_with_local(type_name)
             if not issubclass(obj, MlemABC):
                 raise ValueError(f"{obj} is not subclass of MlemABC")
             return obj
         except ImportError:
             pass
-        finally:
-            sys.path.remove(".")
 
     eps = load_entrypoints()
     for ep in eps.values():

mlem/ext.py

@@ -107,6 +107,11 @@ class ExtensionLoader:
         Extension("mlem.contrib.xgboost", ["xgboost"], False),
         Extension("mlem.contrib.docker", ["docker"], False),
         Extension("mlem.contrib.fastapi", ["fastapi", "uvicorn"], False),
+        Extension(
+            "mlem.contrib.prometheus",
+            ["prometheus-fastapi-instrumentator"],
+            False,
+        ),
         Extension("mlem.contrib.callable", [], True),
         Extension("mlem.contrib.rabbitmq", ["pika"], False, extra="rmq"),
         Extension("mlem.contrib.github", [], True),

mlem/runtime/middleware.py

@@ -0,0 +1,51 @@
+from abc import abstractmethod
+from typing import ClassVar, List
+
+from pydantic import BaseModel
+
+from mlem.core.base import MlemABC
+from mlem.core.requirements import Requirements, WithRequirements
+
+
+class Middleware(MlemABC, WithRequirements):
+    abs_name: ClassVar = "middleware"
+
+    class Config:
+        type_root = True
+
+    @abstractmethod
+    def on_init(self):
+        raise NotImplementedError
+
+    @abstractmethod
+    def on_request(self, request):
+        raise NotImplementedError
+
+    @abstractmethod
+    def on_response(self, request, response):
+        raise NotImplementedError
+
+
+class Middlewares(BaseModel):
+    __root__: List[Middleware] = []
+    """Middlewares to add to server"""
+
+    def on_init(self):
+        for middleware in self.__root__:
+            middleware.on_init()
+
+    def on_request(self, request):
+        for middleware in self.__root__:
+            request = middleware.on_request(request)
+        return request
+
+    def on_response(self, request, response):
+        for middleware in reversed(self.__root__):
+            response = middleware.on_response(request, response)
+        return response
+
+    def get_requirements(self) -> Requirements:
+        reqs = Requirements.new()
+        for m in self.__root__:
+            reqs += m.get_requirements()
+        return reqs

mlem/runtime/server.py

@@ -15,6 +15,7 @@
     InterfaceDescriptor,
     InterfaceMethod,
 )
+from mlem.runtime.middleware import Middlewares
 from mlem.utils.module import get_object_requirements
 
 MethodMapping = Dict[str, str]
@@ -120,6 +121,9 @@ class Config:
     additional_source_files: ClassVar[Optional[List[str]]] = None
     port_field: ClassVar[Optional[str]] = None
 
+    middlewares: Middlewares = Middlewares()
+    """Middlewares to add to server"""
+
     # @validator("interface")
     # @classmethod
     # def validate_interface(cls, value):
@@ -155,8 +159,16 @@ def _get_serializers(
         return arg_serializers, returns
 
     def get_requirements(self) -> Requirements:
-        return super().get_requirements() + get_object_requirements(
-            [self.request_serializer, self.response_serializer, self.methods]
+        return (
+            super().get_requirements()
+            + get_object_requirements(
+                [
+                    self.request_serializer,
+                    self.response_serializer,
+                    self.methods,
+                ]
+            )
+            + self.middlewares.get_requirements()
         )
 
     def get_ports(self) -> List[int]:

mlem/utils/importing.py

@@ -46,6 +46,16 @@ def module_imported(module_name):
     return sys.modules.get(module_name) is not None
 
 
+def import_string_with_local(path):
+    try:
+        # this is needed because if run from cli curdir is not checked for
+        # modules to import
+        sys.path.append(".")
+        return import_string(path)
+    finally:
+        sys.path.remove(".")
+
+
 # Copyright 2019 Zyfra
 # Copyright 2021 Iterative
 #

setup.py

@@ -74,6 +74,7 @@
     "xgboost": ["xgboost"],
     "lightgbm": ["lightgbm"],
     "fastapi": ["uvicorn", "fastapi"],
+    "prometheus": ["prometheus-fastapi-instrumentator"],
     "streamlit": ["uvicorn", "fastapi", "streamlit", "streamlit_pydantic"],
     "sagemaker": ["docker", "boto3", "sagemaker"],
     "torch": ["torch"],
@@ -214,6 +215,7 @@
             "serializer.pil_numpy = mlem.contrib.pil:PILImageSerializer",
             "builder.pip = mlem.contrib.pip.base:PipBuilder",
             "builder.whl = mlem.contrib.pip.base:WhlBuilder",
+            "middleware.prometheus_fastapi = mlem.contrib.prometheus:PrometheusFastAPIMiddleware",
             "client.rmq = mlem.contrib.rabbitmq:RabbitMQClient",
             "server.rmq = mlem.contrib.rabbitmq:RabbitMQServer",
             "builder.requirements = mlem.contrib.requirements:RequirementsBuilder",