metrics and main

Signed-off-by: rafsaf <rafal.safin12@gmail.com>

Author: rafsaf

README.md

@@ -372,7 +372,7 @@ There are some **opinionated** default settings in `/app/main.py` for documentat
     ```python
     app = FastAPI(
         title="minimal fastapi postgres template",
-        version="6.1.0",
+        version="7.0.0",
         description="https://github.com/rafsaf/minimal-fastapi-postgres-template",
         openapi_url="/openapi.json",
         docs_url="/",

app/core/config.py

@@ -47,9 +47,18 @@ class Database(BaseModel):
     db: str = "postgres"
 
 
+class Prometheus(BaseModel):
+    enabled: bool = False
+    port: int = 9090
+    addr: str = "127.0.0.1"
+    stop_delay_secs: int = 0
+
+
 class Settings(BaseSettings):
     security: Security = Field(default_factory=Security)
     database: Database = Field(default_factory=Database)
+    prometheus: Prometheus = Field(default_factory=Prometheus)
+
     log_level: str = "INFO"
 
     @computed_field  # type: ignore[prop-decorator]

app/core/metrics.py

@@ -0,0 +1,20 @@
+import prometheus_client
+
+NAMESPACE = "org"
+SUBSYSTEM = "app"
+
+APP_STARTED = prometheus_client.Counter(
+    "app_started_total",
+    "FastAPI application start count",
+    labelnames=(),
+    namespace=NAMESPACE,
+    subsystem=SUBSYSTEM,
+)
+
+APP_STOPPED = prometheus_client.Counter(
+    "app_stopped",
+    "FastAPI application stop count",
+    labelnames=(),
+    namespace=NAMESPACE,
+    subsystem=SUBSYSTEM,
+)

app/main.py

@@ -1,16 +1,61 @@
+import asyncio
+import logging
+from collections.abc import AsyncGenerator
+from contextlib import asynccontextmanager
+
+import prometheus_client
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.middleware.trustedhost import TrustedHostMiddleware
 
 from app.auth.views import router as auth_router
+from app.core import database_session, metrics
 from app.core.config import get_settings
 
+logger = logging.getLogger(__name__)
+
+
+@asynccontextmanager
+async def lifespan(_: FastAPI) -> AsyncGenerator[None]:
+    logger.info("starting application...")
+    if get_settings().prometheus.enabled:
+        logger.info(
+            "starting prometheus client server on interface %s port %d",
+            get_settings().prometheus.addr,
+            get_settings().prometheus.port,
+        )
+
+        prometheus_client.start_http_server(
+            addr=get_settings().prometheus.addr,
+            port=get_settings().prometheus.port,
+        )
+        metrics.APP_STARTED.inc()
+
+    yield
+
+    logger.info("shutting down application...")
+
+    await database_session._ASYNC_ENGINE.dispose()
+    logger.info("disposed database engine and closed connections...")
+
+    if get_settings().prometheus.enabled:
+        logger.info(
+            "stopping prometheus with delay of %d seconds...",
+            get_settings().prometheus.stop_delay_secs,
+        )
+        metrics.APP_STOPPED.inc()
+        await asyncio.sleep(get_settings().prometheus.stop_delay_secs)
+
+    logger.info("bye! application shutdown completed")
+
+
 app = FastAPI(
     title="minimal fastapi postgres template",
     version="7.0.0",
     description="https://github.com/rafsaf/minimal-fastapi-postgres-template",
     openapi_url="/openapi.json",
     docs_url="/",
+    lifespan=lifespan,
 )
 
 app.include_router(auth_router, prefix="/auth", tags=["auth"])

pyproject.toml

@@ -5,6 +5,7 @@ dependencies = [
     "asyncpg>=0.31.0",
     "bcrypt>=5.0.0",
     "fastapi>=0.128.0",
+    "prometheus-client>=0.24.1",
     "pydantic-settings>=2.12.0",
     "pydantic[email]>=2.12.5",
     "pyjwt>=2.11.0",