fix: add proxy objects

Signed-off-by: Aaron Pham <29749331+aarnphm@users.noreply.github.com>

src/bentoml/metrics.py

@@ -2,6 +2,13 @@
 
 import typing as t
 import logging
+from typing import TYPE_CHECKING
+
+from simple_di import inject
+from simple_di import Provide
+
+if TYPE_CHECKING:
+    from ._internal.server.metrics.prometheus import PrometheusClient
 
 logger = logging.getLogger(__name__)
 
@@ -13,8 +20,41 @@ def __dir__() -> list[str]:
     return dir(metrics_client.prometheus_client)
 
 
+class LazyObject:
+    def __init__(self, attr: t.Any):
+        self.__bentoml_metrics_attr__ = attr
+        self._proxy = None
+        self._initialized = False
+        self._args: tuple[t.Any, ...] = ()
+        self._kwargs: dict[str, t.Any] = {}
+
+    def __call__(self, *args: t.Any, **kwargs: t.Any) -> t.Any:
+        # This is where we lazy load the proxy object.
+        self._args = args
+        self._kwargs = kwargs
+        return self
+
+    def __getattr__(self, item: t.Any) -> t.Any:
+        if self._proxy is None:
+            self._load_proxy()
+        assert self._initialized
+        return getattr(self._proxy, item)
+
+    @inject
+    def _load_proxy(
+        self,
+        metrics_client: PrometheusClient = Provide[BentoMLContainer.metrics_client],
+    ) -> None:
+        parent = (
+            metrics_client
+            if self.__bentoml_metrics_attr__ in dir(metrics_client)
+            else metrics_client.prometheus_client
+        )
+        self._proxy = getattr(parent, self.__bentoml_metrics_attr__)(
+            *self._args, **self._kwargs
+        )
+        self._initialized = True
+
+
 def __getattr__(item: t.Any):
-    metrics_client = BentoMLContainer.metrics_client.get()
-    if item in dir(metrics_client):
-        return getattr(metrics_client, item)
-    return getattr(metrics_client.prometheus_client, item)
+    return LazyObject(item)