Load Balancer Debugging & Extension

Debug and extend a provided load-balancer codebase across four parts: repair failed health checks, diagnose excess latency, add a circuit breaker for unhealthy servers, and replace round-robin routing with least-request-latency selection. Requirements Work in a provided load-balancer codebase and complete four sequential parts: Part 1 — Health-check failure. The load balancer receives repeated HTTP 500 responses. Trace the failure to mismatched hostname and port names in the health-check path, then correct the configuration or lookup so healthy hosts are no longer marked unhealthy. Part 2 — Latency diagnosis. Service latency is above expectations. Find the server path containing an excessive sleep and instrument request latency so the slow path can be identified from measurements rather than guesswork. Part 3 — Circuit breaker. Implement protection that prevents the load balancer from sending requests to servers already considered unhealthy. Part 4 — Routing policy. Replace the existing round-robin policy with a policy that selects the server with the lowest observed request latency. Exact class names, method signatures, and test cases are supplied by the interview codebase and should be confirmed before editing. Notes Root-cause analysis and decision justification carry more weight than raw implementation speed. Narrate what evidence rules hypotheses in or out before changing the code. Part 2 is intentionally straightforward at the code level; the evaluation signal is the debugging method and the latency instrumentation. Keep fault detection, request admission, and backend selection as separate responsibilities so later parts do not require rewriting earlier fixes. Preparation Rehearse reading a small unfamiliar backend codebase: locate the request path, health-check path, backend registry, and routing policy before making changes. Build a minimal load-balancer prototype with pluggable routing, health state, request-latency measurement, and a circuit-breaker gate. Practice explaining each debugging step aloud, including the observation, hypothesis, instrumentation, result, and resulting code change.