Authorizing 10 Million API Calls Per Second

LinkedIn handles authorization for tens of millions of API calls per second using Access Control Lists (ACLs) with an in-memory authorization client on each service. ACL data is stored in Espresso database with Couchbase caching, synchronized via Brooklin change data capture. Authorization checks are logged asynchronously through Kafka for monitoring and auditing. The system balances fast authorization checks, timely ACL updates, efficient data management, and comprehensive monitoring at massive scale.