Fix: add environment variable flag to log alembic to stdout

[HzaRashid]

Introduce a Boolean environment variable flag that will have Alembic to log to stdout if set to True. Default value is False to preserve Langflow's original behavior (logging to alembic.log file).

Fixes the issue in production where alembic logs were not written to stdout in k8s.

Summary by CodeRabbit

New Features

• Added configuration option to direct database migration logs to stdout or file output. Users can enable this feature using the LANGFLOW_ALEMBIC_LOG_TO_STDOUT environment variable to output logs to standard output instead of file-based logging, with file-based logging as the default.

[coderabbitai]

Walkthrough

The changes introduce a new alembic_log_to_stdout configuration flag that allows Alembic database migration logs to be directed to stdout instead of a file. The flag is added to the settings schema and environment configuration, and then applied in the database service's migration runner to conditionally route logs.

Changes

Cohort / File(s)	Summary
Configuration \.env\.example, src/lfx/src/lfx/services/settings/base.py	Added new environment variable and Settings field alembic_log_to_stdout with default value False to control whether Alembic logs to stdout or file.
Database Service src/backend/base/langflow/services/database/service.py	Implemented conditional logging logic: when flag is true, logs to stdout via nullcontext(sys.stdout); otherwise, logs to file with existing path resolution and directory initialization.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

• Simple boolean flag conditionally routing log output between two established patterns (stdout vs. file)
• Configuration field addition is straightforward
• Logic changes in database service follow a clear, repetitive pattern with no complex state management

Pre-merge checks and finishing touches

❌ Failed checks (1 error, 2 inconclusive)

Check name	Status	Explanation	Resolution
Test Coverage For New Implementations	❌ Error	PR adds new Alembic logging feature to database service and settings but includes no corresponding test coverage.	Add tests verifying environment variable parsing, stdout vs file logging modes, and database service initialization with both configurations.
Test Quality And Coverage	❓ Inconclusive	Assessment cannot be completed due to inability to access repository files needed to verify test coverage for the database service changes.	Provide access to test files, complete list of modified files including tests, or confirmation of test coverage for the database service module.
Test File Naming And Structure	❓ Inconclusive	Unable to assess test file naming and structure due to technical limitations preventing repository access and codebase inspection.	Provide direct repository access or supply specific test files included in the PR for manual verification of test naming conventions and structure.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: adding an environment variable flag to enable Alembic logging to stdout, which directly matches the changeset modifications across configuration files and the database service.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Excessive Mock Usage Warning	✅ Passed	No test files were added or modified in this PR, making excessive mock usage assessment not applicable.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (1)

.env.example (1)

25-26: Consider clarifying the comment wording.

The comment refers to this as "Alembic logs path flag" which is slightly unclear. Consider rephrasing to better reflect that this controls the log output destination rather than a path setting.

Suggested wording:

-# Alembic logs path flag. If set to true, Alembic will log to stdout.
+# Alembic log output destination. If set to True, Alembic will log to stdout instead of a file.

📜 Review details

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between d1d005c and 23428fd.

📒 Files selected for processing (3)

• .env.example (1 hunks)
• src/backend/base/langflow/services/database/service.py (3 hunks)
• src/lfx/src/lfx/services/settings/base.py (1 hunks)

🧰 Additional context used

🧠 Learnings (1)

📚 Learning: 2025-08-07T20:23:23.569Z

Learnt from: edwinjosechittilappilly
Repo: langflow-ai/langflow PR: 0
File: :0-0
Timestamp: 2025-08-07T20:23:23.569Z
Learning: The Langflow codebase uses structlog for structured logging with a centralized configuration in `src/backend/base/langflow/logging/logger.py`. The configuration supports multiple output formats (JSON, CSV, console) based on environment settings and properly implements global log level filtering.

Applied to files:

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

🧬 Code graph analysis (1)

src/backend/base/langflow/services/database/service.py (1)

src/backend/tests/unit/api/v2/test_mcp_servers_file.py (1)

• settings_service (96-97)

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🔇 Additional comments (4)

src/lfx/src/lfx/services/settings/base.py (1)

248-249: LGTM!

The new setting is correctly defined with appropriate type annotation, default value, and clear documentation. The placement next to the related alembic_log_file setting makes sense for maintainability.

src/backend/base/langflow/services/database/service.py (3)

6-8: LGTM!

The new imports are appropriate for the implementation. Using nullcontext is the correct approach for wrapping sys.stdout in a context manager without closing it.

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77-82: LGTM!

The early return when logging to stdout is an efficient approach that avoids unnecessary file system operations. The logic correctly handles both stdout and file-based logging scenarios.

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337-341: LGTM!

The buffer context implementation correctly handles both stdout and file-based logging:

• Uses nullcontext(sys.stdout) for stdout logging, which properly wraps stdout without closing it
• Uses file open with "w" mode for file logging, which will be properly closed by the context manager

The file is opened in "w" (truncate) mode, which overwrites the log on each run. This appears intentional to prevent the log file growth issue mentioned in the PR objectives.

[zzzming]

Do we need to update document? Can you also make sure we don't need to /data folder access from alembic point of view?