caching strategies

A deceptively rich warm-up. The interesting decisions are how you generate short, collision-free, unguessable keys at scale, and how a read-heavy 100:1 workload shapes the storage and caching. Here is the clean design with capacity math.

The observability infrastructure question. Interviewers want you to separate the three telemetry types, choose storage that survives massive write volume, and design alerting that fires fast without drowning on-call in noise. Here is the pipeline with retention and cardinality math.

The real-time messaging classic. Interviewers want the delivery path (persistent connections, not polling), the fan-out strategy that does not collapse on large groups, and an ordering and delivery-guarantee story. Here is that design with the fan-out tradeoff that separates seniors.