Capacity Planning

Design a durable, high-throughput message system that decouples producers from consumers: producers append events; many independent consumer groups read them at their own pace, replay history, and survive each other's failures.

This is the Kafka lineage — a partitioned, append-only log, not a transient queue. In scope: publishing to a topic, consuming as part of a group while committing progress, replaying from any offset, and retaining messages for a window or compacting the log (keeping only the latest record per key, dropping older ones).