Fix: add environment variable flag to log alembic to stdout (#10620)

* fix: add flag to log alembic to stdout

fix indentation

refine docs

mypy (db service.py)

* [autofix.ci] apply automated fixes

* [autofix.ci] apply automated fixes (attempt 2/3)

* [autofix.ci] apply automated fixes (attempt 3/3)

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

.env.example

@@ -22,6 +22,9 @@ LANGFLOW_SAVE_DB_IN_CONFIG_DIR=
 # SQLite example:
 LANGFLOW_DATABASE_URL=sqlite:///./langflow.db
 
+# Alembic logs path flag. If set to true, Alembic will log to stdout.
+LANGFLOW_ALEMBIC_LOG_TO_STDOUT=False
+
 
 # mem0 creates a directory 
 # for chat history, vector stores, and other artifacts

src/backend/base/langflow/services/database/service.py

@@ -3,8 +3,9 @@ from __future__ import annotations
 import asyncio
 import re
 import sqlite3
+import sys
 import time
-from contextlib import asynccontextmanager
+from contextlib import asynccontextmanager, nullcontext
 from datetime import datetime, timezone
 from pathlib import Path
 from typing import TYPE_CHECKING
@@ -62,14 +63,20 @@ class DatabaseService(Service):
         else:
             self.engine = self._create_engine()
 
+        # Check if Alembic should log to stdout or a file.
+        # If file, check if the provided path is absolute, cross-platform.
         alembic_log_file = self.settings_service.settings.alembic_log_file
-        # Check if the provided path is absolute, cross-platform.
-        if Path(alembic_log_file).is_absolute():
+        self.alembic_log_to_stdout = self.settings_service.settings.alembic_log_to_stdout
+        if self.alembic_log_to_stdout:
+            self.alembic_log_path = None
+        elif Path(alembic_log_file).is_absolute():
             self.alembic_log_path = Path(alembic_log_file)
         else:
             self.alembic_log_path = Path(langflow_dir) / alembic_log_file
 
     async def initialize_alembic_log_file(self):
+        if self.alembic_log_to_stdout:
+            return
         # Ensure the directory and file for the alembic log file exists
         await anyio.Path(self.alembic_log_path.parent).mkdir(parents=True, exist_ok=True)
         await anyio.Path(self.alembic_log_path).touch(exist_ok=True)
@@ -328,7 +335,10 @@ class DatabaseService(Service):
         # which is a buffer
         # I don't want to output anything
         # subprocess.DEVNULL is an int
-        with self.alembic_log_path.open("w", encoding="utf-8") as buffer:
+        buffer_context = (
+            nullcontext(sys.stdout) if self.alembic_log_to_stdout else self.alembic_log_path.open("w", encoding="utf-8")  # type: ignore[union-attr]
+        )
+        with buffer_context as buffer:
             alembic_cfg = Config(stdout=buffer)
             # alembic_cfg.attributes["connection"] = session
             alembic_cfg.set_main_option("script_location", str(self.script_location))

src/lfx/src/lfx/services/settings/base.py

@@ -245,6 +245,8 @@ class Settings(BaseSettings):
     """The path to log file for Langflow."""
     alembic_log_file: str = "alembic/alembic.log"
     """The path to log file for Alembic for SQLAlchemy."""
+    alembic_log_to_stdout: bool = False
+    """If set to True, the log file will be ignored and Alembic will log to stdout."""
     frontend_path: str | None = None
     """The path to the frontend directory containing build files. This is for development purposes only.."""
     open_browser: bool = False