Kafka's pieces are each simple — partitions, keys, consumer groups, offsets, lag — but together they tie people in knots. So I built an interactive playground where you produce and consume and watch it happen, no broker required.
▶ Live demo: https://dev48v.github.io/kafka-playground/
Source (single file, zero deps): https://github.com/dev48v/kafka-playground
The four ideas, made visible
1. Keys decide partitions. Produce a message with a key and it's hashed to a partition — and the same key always goes to the same partition:
