sla

The POC-to-production gap is the FDE's home turf. What actually breaks at each order of magnitude (index, ingestion, latency, cost) and the dependency math that makes 99.9% harder than it sounds.

The capstone FDE question, where every topic in this category shows up as one workstream. The rubric isn't the target architecture; it's whether you can sequence the gap-closing while the customer keeps using the pilot.

Latency, cost, and quality are one budget with three claims on it. The strong answer treats the p99 SLA and the spend ceiling as a joint constraint, finds where they fight (batching), and names the lever it pulls when traffic exceeds what the ceiling can buy at SLA.

A 4-hour outage is ~5.6x your entire monthly error budget on a 99.9% SLA. You cannot ride it out. The design is a provider abstraction, a circuit breaker, and a tiered set of degraded modes, plus a clear line on what you cache versus what you replay.