add alembic and store metrics at db

src/main.py

@@ -1,17 +1,24 @@
+import socket
 from typing import Callable
 
 from fastapi import FastAPI
-from prometheus_client import Counter
+from prometheus_client import Gauge
 from prometheus_fastapi_instrumentator import Instrumentator
 from prometheus_fastapi_instrumentator.metrics import Info
+from sqlalchemy.orm.session import Session
 
-REQUEST_COUNT = Counter(
+import models
+
+REQUEST_COUNT = Gauge(
     "label_counter", "How many times called with specific label", labelnames=("label",)
 )
 
 
 def http_requested_languages_total() -> Callable[[Info], None]:
-    def instrumentation(info: Info) -> None: ...
+    def instrumentation(info: Info) -> None:
+        with Session(models.engine) as session:
+            for label_info in models.LabelUsageRecord.get_all_stats(session=session):
+                REQUEST_COUNT.labels(label_info.label).set(label_info.used_count)
 
     return instrumentation
 
@@ -23,5 +30,13 @@ Instrumentator().add(http_requested_languages_total()).instrument(app).expose(ap
 @app.get("/")
 async def read_root(label=None):
     if label:
-        REQUEST_COUNT.labels(label).inc()
-    return {"Hello": "World"}
+        with Session(models.engine) as session:
+            models.LabelUsageRecord.update_label_usage_record(label, session=session)
+            session.commit()
+    return {"Hello": "World", "from": socket.gethostname()}
+
+
+@app.get("/test")
+async def read_label(label):
+    with Session(models.engine) as session:
+        return models.LabelUsageRecord.get_label_usage_record(label, session=session)

src/models.py

@@ -0,0 +1,43 @@
+import os
+import time
+from typing import List
+
+from sqlalchemy import Boolean, Column, Integer, String, create_engine, select
+from sqlalchemy.orm import DeclarativeBase
+from sqlalchemy.orm.session import Session
+
+engine = create_engine(os.getenv("DATABASE_URL"), echo=True)
+
+
+class BaseModel(DeclarativeBase):
+    pass
+
+
+class LabelUsageRecord(BaseModel):
+    __tablename__ = "label_usage_stats"
+
+    label = Column(String, primary_key=True)
+    last_used = Column(Integer, nullable=False)
+    used_count = Column(Integer)
+
+    @staticmethod
+    def get_label_usage_record(label, session: Session):
+        stmt = select(LabelUsageRecord).where(LabelUsageRecord.label == label)
+        result = session.scalar(stmt)
+
+        if not result:
+            result = LabelUsageRecord(label=label, last_used=0, used_count=0)
+
+        return result
+
+    @staticmethod
+    def update_label_usage_record(label: str, session: Session):
+        usage = LabelUsageRecord.get_label_usage_record(label, session=session)
+        usage.used_count += 1
+        usage.last_used = int(time.time())
+        session.add(usage)
+
+    @staticmethod
+    def get_all_stats(session: Session) -> List[LabelUsageRecord]:
+        stmt = select(LabelUsageRecord)
+        return session.scalars(stmt)