start project

app/logging_setup.py

@@ -0,0 +1,34 @@
+"""Structured stdout/stderr logging (Chapter 02 factor 11 / Chapter 12).
+
+Writes structured (key=value) lines to stdout so the host's log capture
+picks them up, per 12-factor logs. Falls back to a size-capped rotating
+file only if LOG_FALLBACK_FILE is explicitly set (Ch12: "if stdout capture
+is unavailable on the specific hosting setup").
+"""
+from __future__ import annotations
+
+import logging
+import os
+import sys
+from logging.handlers import RotatingFileHandler
+
+from flask import Flask
+
+_FORMAT = "%(asctime)s level=%(levelname)s logger=%(name)s msg=%(message)s"
+
+
+def configure_logging(app: Flask) -> None:
+    formatter = logging.Formatter(_FORMAT)
+
+    stdout_handler = logging.StreamHandler(sys.stdout)
+    stdout_handler.setFormatter(formatter)
+
+    app.logger.handlers = [stdout_handler]
+    app.logger.setLevel(logging.INFO if not app.debug else logging.DEBUG)
+    app.logger.propagate = False
+
+    fallback_path = os.environ.get("LOG_FALLBACK_FILE")
+    if fallback_path:
+        file_handler = RotatingFileHandler(fallback_path, maxBytes=5 * 1024 * 1024, backupCount=3)
+        file_handler.setFormatter(formatter)
+        app.logger.addHandler(file_handler)