Design a Smooth Per-Customer Calls-Per-Second Controller
Company: Retell AI
Role: Software Engineer
Category: System Design
Difficulty: medium
Interview Round: Technical Screen
Overview: Design a service that smoothly paces outbound calls under a separate rate limit for each customer. Candidates must address durable admission, priority fairness, tenant isolation, partition ownership, failover fencing, retries, backpressure, and observable delivery semantics.