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API Gateway System Design
Visual Problem Diagram
Scenario
A misconfigured route sends payment traffic through the debug plugin and every checkout times out at p99 8 s—meanwhile one OAuth client hammers a single shard because rate limits lived in app code, not the edge. The gateway interview is routing, auth, rate limits, and observability on the shared front door.
Design an API gateway that sits in front of microservices and handles routing, authentication, rate limiting, SSL termination, and optional request aggregation. It is the shared failure domain for misconfigurations and overload—design for HA, low added latency, and clear HTTP contracts.
You should support dynamic routing, JWT/API-key auth, per-client rate limits, logging/metrics, and circuit breaking to backends. Be ready to compare with load balancers, explain distributed rate limiting, and how config changes roll out safely.
Constraints
Route by path/host/header, JWT and API key auth, rate limiting, SSL termination, request/response transform, metrics
< 5 ms added p99, 99.99% availability, zero-downtime config, handle 100K+ RPS per region
10K+ routes, 100K RPS peak, thousands of tenants/API keys, global multi-region
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