Exercise 2: Implement Redis Sliding Window Rate Limiter

[harsharajkumar-273]

Goal

Protect the ingestion gateway from volumetric traffic surges and DDoS attacks.

Problem

There is currently no rate limiting on the /v1/events endpoint. A single malicious client can flood the gateway, causing resource exhaustion across Redpanda and PostgreSQL.

Task

1. Implement a rate limiter in src/middleware/rateLimiter.ts using Redis sorted sets (zsets).
2. Maintain a sliding-window duration of 60 seconds allowing a maximum of 100 requests.
3. Execute the Redis operations atomically using a multi-pipeline transaction (ZREMRANGEBYSCORE, ZADD, ZCARD, EXPIRE).
4. Return an HTTP 429 status code with a 'Retry-After' header if the count is exceeded.