19-Usage-Billing-Engine

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14.10 API Design & Rate Limiting ​

1. What It Is in Plain Words ​

Rate limiting restricts the number of requests a client can submit within a time window, protecting backend databases from denial-of-service traffic spikes.

2. How This Project Uses It ​

  • Token Bucket Algorithm: Implemented in Redis, allowing burst traffic while enforcing sustained QPS limits per tenant API key.
  • Batch Endpoints: POST /v1/usage/events/batch accepting up to 1,000 events to minimize HTTP connection overhead.

3. 30-Second Interview Answer ​

"We enforce rate limiting using the Token Bucket algorithm stored in Redis. Each tenant is allocated a burst capacity of 1,000 tokens replenishing at 200 tokens per second. If a client exceeds their quota, the API returns a 429 Too Many Requests response with a Retry-After header, protecting database workers from runaway scripts."