Good Design Pays Dividends: The Evolution of LINE API Gateway Handling 30B Daily Requests

30 billion requests per day. That's the scale of LINE's API Gateway after 15 years in production. As traffic grew, new challenges appeared. Latency in a single backend could affect the entire API layer. Adding even a simple API required code changes, and hundreds of API documents gradually drifted away from the implementation.

To solve these problems, we built Moon, an API Gateway framework based on declarative API specifications, asynchronous processing, and a plugin architecture. The result was 3× higher throughput per server and the ability to add APIs without restarting servers.

It wasn't just about performance. The same API specifications are now used for documentation, traffic-based validation, and AI tooling. This session covers the design of Moon and how solving infrastructure challenges opened the door to new capabilities.