Book 2 · Lesson 2.7

Backpressure and replayability

Prerequisites: 2.6

When producers outpace consumers, lag grows — that is backpressure visible in metrics.

Offsets

KafkaOffsetRewind — burst +5 messages, consume one-by-one, or replay from offset 0.

Action	Dev	Prod
Reset consumer group	Reprocess test data	Dangerous — duplicate side effects
Scale consumers	Add llm-worker replicas	Same

Replay requires idempotent writes (e.g. upsert by event id) or you duplicate Postgres rows.

How would you alert when lag exceeds 1000 messages?

1. Consumer lag means… Browser is slow Consumers behind producers TLS expired WASM failed