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

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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"])

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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.

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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.

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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)

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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