caching strategies

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

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

The real-time messaging staple. Interviewers look for the delivery path (persistent connections, not polling), a fan-out strategy that survives large groups, and a clear story on ordering and delivery guarantees. This lays out that design, including the fan-out tradeoff that marks senior candidates.