A survival guide for when everything goes wrong in production.
There's a moment every engineer who works with Kafka experiences. You check the producer. Messages are sending. You check the consumer. Nothing. The consumer group shows zero lag because there's nothing to lag behind — as far as the consumer knows, the topic is empty.
But it's not empty. The messages are there. Somewhere. In some partition, at some offset, behind some configuration you set six months ago and forgot about.
Kafka doesn't lose messages. But it's very good at hiding them from you.
Consumer Lag: The Number Everyone Watches Wrong
