Separate fastapi app instance from main module to ensure there is onl…

…y one app instance is generated

ref: https://stackoverflow.com/questions/70300675/fastapi-uvicorn-run-always-create-3-instances-but-i-want-it-1-instance

app/app.py

@@ -0,0 +1,50 @@
+import logging
+import logging.config
+import logging.handlers
+from contextlib import asynccontextmanager
+
+from asgi_correlation_id import correlation_id, CorrelationIdMiddleware
+from fastapi import FastAPI, HTTPException, Request
+from fastapi.exception_handlers import http_exception_handler
+from starlette.responses import Response
+
+import log_config
+from routers import demo, heavy_task
+
+
+def find_log_file_handler() -> logging.Handler:
+    # ref: https://stackoverflow.com/a/55400327/11397457
+    l = logging.Logger.manager.loggerDict["uvicorn"]
+    for h in l.handlers:
+        if isinstance(h, logging.handlers.TimedRotatingFileHandler):
+            return h
+    raise Exception("Can not found file handler.")
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    # We must configure app logging after uvicorn started, thus the file handler should exists for reusing.
+    log_config.configure_app_logging(find_log_file_handler())
+    global log
+    log = logging.getLogger(__name__)
+    yield
+
+
+app = FastAPI(lifespan=lifespan)
+app.include_router(demo.router)
+app.include_router(heavy_task.router)
+app.add_middleware(CorrelationIdMiddleware)
+
+
+@app.exception_handler(Exception)
+async def unhandled_exception_handler(request: Request, exc: Exception) -> Response:
+    """
+    ref: https://github.com/snok/asgi-correlation-id?tab=readme-ov-file#fastapi-1
+    """
+    return await http_exception_handler(
+        request,
+        HTTPException(
+            500,
+            'Internal server error',
+            headers={'X-Request-ID': correlation_id.get() or ""}
+        ))

app/main.py

@@ -1,59 +1,12 @@
-import logging
-import logging.config
 import logging.handlers
-from contextlib import asynccontextmanager
 
 import uvicorn
-from asgi_correlation_id import correlation_id, CorrelationIdMiddleware
-from fastapi import FastAPI, HTTPException, Request
-from fastapi.exception_handlers import http_exception_handler
-from starlette.responses import Response
 from uvicorn.config import LOGGING_CONFIG
 
 import log_config
-from routers import demo
 
 log: logging.Logger
 
-FILE_HANDLER_NAME = "file_handler"
-
-
-def find_log_file_handler() -> logging.Handler:
-    # ref: https://stackoverflow.com/a/55400327/11397457
-    l = logging.Logger.manager.loggerDict["uvicorn"]
-    for h in l.handlers:
-        if isinstance(h, logging.handlers.TimedRotatingFileHandler):
-            return h
-    raise Exception("Can not found file handler.")
-
-
-@asynccontextmanager
-async def lifespan(app: FastAPI):
-    # We must configure app logging after uvicorn started, thus the file handler should exists for reusing.
-    log_config.configure_app_logging(find_log_file_handler())
-    global log
-    log = logging.getLogger(__name__)
-    yield
-
-
-app = FastAPI(lifespan=lifespan)
-app.include_router(demo.router)
-app.add_middleware(CorrelationIdMiddleware)
-
-
-@app.exception_handler(Exception)
-async def unhandled_exception_handler(request: Request, exc: Exception) -> Response:
-    """
-    ref: https://github.com/snok/asgi-correlation-id?tab=readme-ov-file#fastapi-1
-    """
-    return await http_exception_handler(
-        request,
-        HTTPException(
-            500,
-            'Internal server error',
-            headers={'X-Request-ID': correlation_id.get() or ""}
-        ))
-
 
 def configure_uvicorn_logging():
     """Must configure the uvicorn.config.LOGGING_CONFIG within the same module that runs uvicorn.run()."""
@@ -63,15 +16,17 @@ def configure_uvicorn_logging():
     for formatter in LOGGING_CONFIG["formatters"].values():
         formatter["fmt"] = log_config.LOG_FORMAT_PATTERN
 
-    LOGGING_CONFIG["handlers"][FILE_HANDLER_NAME] = log_config.FILE_HANDLER_CONFIG
+    file_handler_name = "file_handler"
+    LOGGING_CONFIG["handlers"][file_handler_name] = log_config.FILE_HANDLER_CONFIG
+
     # There are three loggers in uvicorn default logging config: "uvicorn", "uvicorn.access", "uvicorn.error".
     # We need to add "file_handler" to logger "uvicorn" and "uvicorn.access"
     # since logger "uvicorn.error" will propagate the log to the other two.
     for logger in LOGGING_CONFIG["loggers"].values():
         if "handlers" in logger:
-            logger["handlers"] += [FILE_HANDLER_NAME]
+            logger["handlers"] += [file_handler_name]
 
 
 if __name__ == "__main__":
     configure_uvicorn_logging()
-    uvicorn.run("main:app", port=8000, reload=True)
+    uvicorn.run("app:app", port=8000, reload=True)