02 - Backend Architecture

Overview

Tradeboard uses Flask 3.1 with Flask-RESTX, Flask-SocketIO, Flask-Limiter, Flask-WTF CSRF, SQLAlchemy, APScheduler, DuckDB, ZeroMQ, and a separate asyncio WebSocket proxy. Python >=3.12 is required.

The backend is a single-user application. Production runs Gunicorn with a single eventlet worker (start.sh passes --worker-class eventlet --workers 1), and the market-data proxy runs outside it in its own process. Process-local components such as caches and the EventBus are therefore per process, not shared. Cross-process market-data and selected cache invalidation paths use ZeroMQ.

Request Surfaces

Surface	Registration	Authentication
REST v1	restx_api/__init__.py, prefix /api/v1	Tradeboard API key; CSRF exempt
Session APIs and webhooks	blueprints/*.py	Flask session, webhook secret, or explicit exemption
React bundle	blueprints/react_app.py	Route-specific frontend/auth gates
Socket.IO	extensions.py and subscribers	Flask/Socket.IO lifecycle
Market-data WebSocket	websocket_proxy/server.py, port 8765	Authenticate action with API key
Remote MCP	Conditional in app.py	OAuth 2.1 bearer tokens

Flask-RESTX's Swagger UI is intentionally disabled through doc=False. The API documentation is the maintained external contract.

Application Factory

create_app() initializes Flask, Socket.IO, EventBus subscribers, CSRF, limiter, CORS, CSP, security middleware, traffic/latency/health hooks, React routes, RESTX, feature blueprints, the broker keepalive service, and the real-time order-update adapters. The scoped-session teardown handler is registered at module scope after the factory returns. Remote MCP blueprints are imported and registered only when MCP_HTTP_ENABLED=True passes startup safety checks.

Service Flow

HTTP resource or blueprint
        |
        v
schema/session validation
        |
        v
service orchestration
   |          |          |
   v          v          v
live broker  sandbox   Action Center
module       manager   pending execution
        |
        v
typed EventBus events -> log / Socket.IO / Telegram / WhatsApp / proxy-relay / strategy-book subscribers

Order services strip sensitive fields before logging events. Analyzer mode routes supported operations to sandbox managers. Semi-auto mode queues eligible operations in Action Center and blocks specific destructive calls according to each service's policy.

Persistence

SQLAlchemy modules use scoped sessions and NullPool for SQLite. utils/db_sessions.py owns the registry of every scoped session; app.py's teardown_appcontext handler calls remove_all_scoped_sessions() after each request, and background threads that run without an app context call the same function themselves. Historify owns a separate DuckDB file and its own connection discipline. See 18 Database Structure.

Background Components

• APScheduler jobs for Flow, Python strategies, Historify, and maintenance paths.
• Sandbox execution, square-off, and settlement workers.
• Broker keepalive service.
• Real-time order-update adapters that ingest broker order pushes or postbacks and republish them as order.update events.
• Scalping risk monitor that subscribes to live ticks and survives browser navigation.
• Telegram/WhatsApp service startup when configured.
• WebSocket proxy process under eventlet/gunicorn, or OS thread in direct development startup.
• Health metrics and database initialization work.

Security Boundaries

• APP_KEY and API_KEY_PEPPER are startup requirements.
• Broker tokens and retrievable API keys are Fernet-encrypted; API-key verification uses Argon2 plus a pepper.
• Session routes retain CSRF except explicit broker-callback, webhook, postback, and health exemptions. auth.logout is deliberately not exempt.
• /api/v1 is CSRF-exempt because it uses API-key authentication.
• CORS, CSP, proxy-header trust, IP bans, cookie security, and session expiry are environment controlled.
• Debug mode on a non-loopback host is refused unless explicitly overridden; Remote MCP refuses debug mode.

Key Files

File	Purpose
app.py	Factory, registration, setup, startup
restx_api/__init__.py	Public v1 namespace registry
blueprints/react_app.py	SPA serving and route aliases
services/order_router_service.py	Auto/semi-auto routing
utils/plugin_loader.py	Broker discovery and lazy auth imports
database/engine_factory.py	SQLite engine policy
utils/db_sessions.py	Scoped-session registry and release
utils/event_bus.py	Per-process async event dispatch
websocket_proxy/app_integration.py	Proxy lifecycle selection