Problems / LLM serving, easy

AI gateway key limit

All traffic goes through an AI gateway whose API key allows 1,500 requests a minute. Traffic is 40 a second.

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Your goals

Success ≥ 99%, time to first token p99 ≤ 2.5 s.

Test cases

Like a coding problem, a solution has to pass every case, not just the one it was built for. Submit in the lab runs all 6; 2 of them are hidden until then.

  1. As given. The problem’s own traffic, scheduled failures and seed.
  2. Peak hour. 25% more traffic than the problem states, with the same failures.
  3. A slow dependency. The main data store or model answers twice as slowly for part of the run.
  4. A server dies. One replica of the service with the most replicas is killed for part of the run.

The traffic

40 requests a second for 30 seconds: 100% request (reads).

The system

What each component does in this design, and what calls it. The simulator mimics each one from these settings.

ComponentIts job hereSettings
AI gatewayAI gatewayTraffic enters here.Calls Load balancer.An AI gateway sits in front of model providers to add keys, quotas, logging and fallbacks.100000 slots · 1,500 calls/min
Load balancerLoad balancerAI gateway forwards to it.Calls AI app.Layer 4 balancers route by IP and port; layer 7 balancers read HTTP and can route by path or header.–
AI appApp serviceLoad balancer forwards to it.Calls Model.Little's law: throughput ≈ concurrency ÷ latency. 200 slots at 50 ms serve about 4,000 req/s.3 replicas × 500 slots · timeout 30 s
ModelLLM endpointAI app calls it.Latency has two parts: time to the first token, then a steady stream of tokens per second.400 streams

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