What methods can be used to prevent or reduce the impact of DoS attacks?

To prevent or mitigate the impact of DoS attacks, the following methods can be used:

• Traffic filtering: blocking suspicious IP addresses or geographic regions.
• Rate limiting: restricting the number of requests from a single client within a certain time frame.
• Using CDN and load balancers: distributing the load among servers, which reduces the effect of the attack.
• Authentication and CAPTCHAs: verifying that requests come from real users.
• Monitoring and alerts: timely detection of anomalies in traffic.
• Resource reservation: allocating additional resources to handle peak loads.

An example of simple rate limiting in Python using Flask and the Flask-Limiter library:

from flask import Flask
from flask_limiter import Limiter
from flask_limiter.util import get_remote_address

app = Flask(__name__)
limiter = Limiter(app, key_func=get_remote_address)

@app.route("/")
@limiter.limit("5 per minute")  # no more than 5 requests per minute from one IP

def index():
    return "Hello, world!"

if __name__ == "__main__":
    app.run()

This helps reduce the load from malicious actors attempting to overload the service.