Fixed window algorithm in Rest API - Mini Project: Build & Apply

Implementing Fixed Window Rate Limiting Algorithm

📖 Scenario: You are building a simple REST API server that limits how many requests a user can make in a fixed time window. This helps prevent abuse and keeps the server stable.

🎯 Goal: Build a fixed window rate limiter that counts requests per user in a 60-second window and blocks requests exceeding the limit.

📋 What You'll Learn

Create a dictionary to store request counts per user

Add a variable for the fixed window duration in seconds

Implement the fixed window logic to count requests and reset counts after the window expires

Print whether a request is allowed or blocked based on the rate limit

💡 Why This Matters

🌍 Real World

Rate limiting is used in APIs to prevent too many requests from one user, protecting servers from overload and abuse.

💼 Career

Understanding rate limiting algorithms is important for backend developers and API designers to build reliable and secure services.

1

Create the request count storage

Create a dictionary called request_counts to store the number of requests per user. Initialize it as an empty dictionary.

Rest API

# Create a dictionary called request_counts to store user request counts
# Your code here

Need a hint?

Use curly braces {} to create an empty dictionary in Python.

2

Set the fixed window duration

Create a variable called window_duration and set it to 60 to represent the fixed window length in seconds.

Rest API

request_counts = {}
# Create a variable window_duration and set it to 60
# Your code here

Need a hint?

Just assign the number 60 to the variable window_duration.

3

Implement the fixed window logic

Write a function called is_request_allowed(user_id, current_time) that uses request_counts and window_duration to count requests per user. If the user has made fewer than 5 requests in the current window, increase the count and return True. Otherwise, return False. Use a dictionary value as a tuple (window_start_time, count) to track the window start and count.

Rest API

request_counts = {}
window_duration = 60
# Write the function is_request_allowed(user_id, current_time) below
# Your code here

Need a hint?

Use the current time to check if the window expired. Reset count if expired, else increment if under limit.

4

Test and print the rate limiter result

Call is_request_allowed('user1', 100) five times and print the result each time. Then call it a sixth time and print the result. This shows the limiter blocking the sixth request.

Rest API

request_counts = {}
window_duration = 60

def is_request_allowed(user_id, current_time):
    if user_id not in request_counts:
        request_counts[user_id] = (current_time, 1)
        return True
    window_start, count = request_counts[user_id]
    if current_time - window_start < window_duration:
        if count < 5:
            request_counts[user_id] = (window_start, count + 1)
            return True
        else:
            return False
    else:
        request_counts[user_id] = (current_time, 1)
        return True

# Call is_request_allowed 6 times for 'user1' at time 100 and print results
# Your code here

Need a hint?

Use a for loop to call the function 6 times and print the results with the request number.