Middleware

BackAnt’s app.py wires up several pieces of middleware and lifecycle hooks at application creation time inside create_app().

CORS

Cross-Origin Resource Sharing is enabled globally via flask-cors:

from flask_cors import CORS

app = Flask(__name__)
app.config["CORS_HEADERS"] = "Content-Type"
CORS(app)

This allows all origins by default. To restrict to specific origins, pass an origins argument:

CORS(app, origins=["https://yourfrontend.com"])

Database session teardown

SQLAlchemy uses a scoped session tied to the request context. After each request completes (with or without an exception), the session is removed to prevent connection leaks:

@app.teardown_appcontext
def shutdown_session(exception=None):
    db_session.remove()

db_session is the scoped_session created in startup/Alchemy.py. The remove() call closes the connection and returns it to the pool.

Error handler

APIException is registered as a Flask error handler so any raised APIException anywhere in the request lifecycle is automatically caught and returned as a JSON response:

from helper.execution_tracking.APIException import APIException

@app.errorhandler(APIException)
def invalid_api_usage(exception):
    return jsonify(exception.to_dict()), exception.status_code

See Error Handling for how to raise and use APIException.

Graceful shutdown (SIGTERM)

The app registers a SIGTERM signal handler so it can finish in-flight requests before exiting — important when running inside Docker or Kubernetes:

import signal

def shutdown(signum, frame):
    print("Caught SIGTERM, shutting down")
    exit(0)

signal.signal(signal.SIGTERM, shutdown)

Adding custom middleware

To add your own middleware (e.g. request logging, rate limiting), use Flask’s before_request and after_request hooks inside create_app():

@app.before_request
def log_request():
    myLogger.info(f"{request.method} {request.path}")

@app.after_request
def add_headers(response):
    response.headers["X-Content-Type-Options"] = "nosniff"
    return response

CLI Reference

Architecture

The Basics

Security

Database

External APIs

CORS

Database session teardown

Error handler

Graceful shutdown (SIGTERM)

Adding custom middleware

​CORS

​Database session teardown

​Error handler

​Graceful shutdown (SIGTERM)

​Adding custom middleware

CORS

Database session teardown

Error handler

Graceful shutdown (SIGTERM)

Adding custom middleware