Addresses: Backend session cache not cluster-safe (multi-worker issue)
Problem:
- Session cache is process-local (InMemorySessionCache)
- Multi-worker deployments (uvicorn --workers N) create separate processes
- Each process has its own independent session cache
- Sessions cached in Worker A are invisible to Workers B, C, D
- Users randomly logged out when requests land on different workers
- Also affects RuntimeState, rate limiter, and background jobs
Solution (Option A - Strict single-worker enforcement):
- Enhance startup validation with clearer error messages
- Update error messages to explain the problem and how to fix it
- Document single-worker requirement prominently in Docker configs
- Update module docstrings to clarify constraints
Changes:
1. app/startup.py:
- Enhanced _check_single_worker_mode() error message with troubleshooting
- Enhanced _stage_check_worker_mode_and_acquire_lock() error message
- Removed unused import
2. app/utils/session_cache.py:
- Updated module docstring to explain constraints more clearly
- Added references to deployment documentation
- Clarified multi-worker solution for future implementation
3. app/utils/runtime_state.py:
- Updated module docstring with deployment constraint references
- Aligned messaging with session_cache.py
4. Docker/Dockerfile.backend:
- Added comprehensive comments about single-worker requirement
- Explained impact in multi-worker deployments
- Referenced deployment constraints documentation
5. Docker/docker-compose.yml, compose.prod.yml, compose.debug.yml:
- Added documentation comments about BANGUI_WORKERS constraint
- Explained why single-worker is required
6. backend/tests/test_startup_integration.py:
- Fixed test unpacking to match function return signature (3 values, not 2)
This ensures multi-worker deployments fail loudly at startup with clear
guidance on what went wrong and how to fix it. The database-backed scheduler
lock provides defense-in-depth for container orchestration scenarios.
For future multi-worker support, implement:
- Redis or database-backed session cache
- Shared RuntimeState coordination
- Distributed APScheduler backend
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
- Add _check_single_worker_mode() to startup.py that detects and rejects
multi-worker configurations, raising a clear RuntimeError with instructions
- Set BANGUI_WORKERS=1 as default in Dockerfile.backend
- Document single-worker requirement in compose.prod.yml
- Add 'Deployment Constraints' section to Architekture.md explaining why
single-worker mode is required and detailing future multi-worker support
- Add '9.1 Background Tasks and Scheduler Architecture' section to
Backend-Development.md documenting task structure and single-worker requirement
- Add comprehensive test suite (test_startup.py) covering all scenarios:
allows single worker, rejects multi-worker, validates config format,
and verifies informative error messages
This fix addresses TASK-002 which identified that in-process APScheduler is
unsafe in multi-worker deployments due to each worker creating independent
scheduler instances, causing duplicate background job execution.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
