System Design

How the round runs: scoping, estimation, API contracts, latency numbers, and availability math.

DNS, CDNs, load balancers, gateways, and the protocols between the user and your first service.

Relational and non-relational stores, how indexes work, transaction guarantees, and choosing a store.

Cache patterns, eviction, invalidation, and the ways caches fail.

CAP and PACELC, consistency models, quorums, consensus, clocks, and distributed transactions.

Statelessness, sharding, consistent hashing, replication, hot spots, and multi-region.

Queues and logs, delivery guarantees, backpressure, fan-out, change data capture, and stream processing.

Identity, authorization, encryption, abuse control, privacy law, and tenant isolation.

Redundancy and failover, resilience patterns, rate limiting, deploys, observability, and disaster recovery.

IDs, KV stores, locks, search, geo, counters, feeds, schedulers, and payments.

LLM serving, retrieval, vector search, agent memory, tool harnesses, orchestration, evals, and AI security.

Open-ended prompts with no multiple choice. Draw the architecture, get a structural score, then compare with a sample answer.