Concepts
The building blocks you should be able to combine.
Caching
TTL, invalidation, hot keys, and cache-aside vs write-through.
Queues
Async processing, retries, idempotency, backpressure.
Storage
RDBMS vs NoSQL, indexing, replication, and consistency.
Sharding
Keys, resharding, hotspots, and routing.
CDN
Edge caching, origin strategy, and content freshness.
Observability
SLOs, dashboards, tracing, alerting, and failure drills.
Drill
For any prompt, write down: top 3 bottlenecks, top 3 failures, and one mitigation per item. Do it before drawing boxes.