add custom metric

src/main.py

@@ -1,8 +1,27 @@
+from typing import Callable
+
 from fastapi import FastAPI
+from prometheus_client import Counter
+from prometheus_fastapi_instrumentator import Instrumentator
+from prometheus_fastapi_instrumentator.metrics import Info
+
+REQUEST_COUNT = Counter(
+    "label_counter", "How many times called with specific label", labelnames=("label",)
+)
+
+
+def http_requested_languages_total() -> Callable[[Info], None]:
+    def instrumentation(info: Info) -> None: ...
+
+    return instrumentation
+
 
 app = FastAPI()
+Instrumentator().add(http_requested_languages_total()).instrument(app).expose(app)
 
 
 @app.get("/")
-async def read_root():
+async def read_root(label=None):
+    if label:
+        REQUEST_COUNT.labels(label).inc()
     return {"Hello": "World"}