Design a High-Availability Load Balancer
Company: Amazon
Role: Software Engineer
Category: System Design
Difficulty: hard
Interview Round: Onsite
Design a load balancer that routes HTTP and HTTPS traffic to a fleet of backend service instances across multiple availability zones. The system should support high request volume, low added latency, backend health checks, weighted traffic distribution, graceful removal of unhealthy or draining instances, observability, and no single point of failure. Discuss the API or configuration model, high-level architecture, request flow, routing algorithms, failure handling, scaling strategy, and key trade-offs.
Quick Answer: This question evaluates understanding of load balancing, high-availability architecture, distributed systems, networking, reliability, and operational concerns such as health checks, weighted routing, graceful instance removal, and observability.
