Rate limiting with sliding window in Redis - Mini Project: Build & Apply

Rate Limiting with Sliding Window in Redis

📖 Scenario: You are building a web service that needs to limit how many requests a user can make in a short time to prevent overload and abuse.We will use Redis to implement a sliding window rate limiter that tracks requests per user in real-time.

🎯 Goal: Create a Redis data structure and commands to track user requests and enforce a sliding window rate limit of 5 requests per 10 seconds.

📋 What You'll Learn

Create a Redis sorted set to store timestamps of user requests

Add a configuration variable for the time window size (10 seconds)

Write a Redis command sequence to remove old requests outside the window

Add a command to count current requests and allow or deny new requests based on the limit

💡 Why This Matters

🌍 Real World

Rate limiting protects web services from too many requests in a short time, preventing overload and abuse.

💼 Career

Understanding Redis data structures and commands for rate limiting is valuable for backend developers and system engineers.

1

Create a Redis sorted set key for user requests

Create a Redis sorted set key named user:123:requests to store timestamps of requests for user ID 123. Use the current Unix timestamp in seconds as the score and member. Add one request with timestamp 1000.

Redis

# Your code here

Need a hint?

Use the ZADD command with the key user:123:requests, score 1000, and member 1000.

2

Set the sliding window size configuration

Create a Redis string key named rate_limit:window and set its value to 10 to represent the sliding window size in seconds.

Redis

ZADD user:123:requests 1000 1000
# Your code here

Need a hint?

Use the SET command with key rate_limit:window and value 10.

3

Remove old requests outside the sliding window

Write a Redis command to remove all entries from user:123:requests with scores less than 990 (current timestamp 1000 minus window size 10). Use the ZREMRANGEBYSCORE command.

Redis

ZADD user:123:requests 1000 1000
SET rate_limit:window 10
# Your code here

Need a hint?

Use ZREMRANGEBYSCORE with -inf as the minimum and 989 as the maximum score.

4

Check current request count and add new request if allowed

Use ZCARD user:123:requests to get the current number of requests in the window. If the count is less than 5, add a new request with timestamp 1001 using ZADD. Otherwise, do not add the request.

Redis

ZADD user:123:requests 1000 1000
SET rate_limit:window 10
ZREMRANGEBYSCORE user:123:requests -inf 989
# Your code here

Need a hint?

Use ZCARD to count requests and ZADD to add the new request if count < 5.