shaf65/request_throttler_interceptor

Request Throttling Interceptor with Redis

This Ballerina interceptor throttles HTTP requests based on a sliding window algorithm using Redis as the backing store. The interceptor limits the number of requests a client can send within a specific time window.

Configuration

The interceptor supports the following configurable values:

• redistHost: The Redis server's host (default: localhost).
• redistPort: The Redis server's port (default: 6379).
• WINDOW_SIZE: The size of the time window in seconds (default: 15 seconds).
• MAX_REQUESTS: The maximum number of requests allowed within the time window (default: 5 requests).

Request Throttler Interceptor

The RequestThrottlerRedisInceptor service class implements request interception to limit incoming HTTP requests using Redis.

• Redis Client: A Redis client (redis:Client) is initialized in the init function to communicate with the Redis server.
• Resource Function:
  • The default resource is triggered for any incoming requests.
  • It checks whether the request should be allowed or throttled by calling the allowRequest() function.
  • If the request is allowed, it proceeds to the next service using ctx.next().
  • If the request exceeds the rate limit, a HTTP 429 Too Many Requests response is returned.

Request Validation Logic

The core logic to determine whether a request is allowed is implemented in the allowRequest function, which follows these steps:

1. Get Last Served Requests:

   • Fetches the most recent request timestamps from Redis using getLastFewRequestWithOffset().

2. Filter Old Requests:

   • Removes requests that are older than the configured WINDOW_SIZE using removeOldRequests().

3. Check Window Status:

   • Determines if the sliding window has room for more requests using isWindowNotFull().

4. Push Current Request:

   • If the window is not full, the current request timestamp is added to the Redis list.