Kafka acks=all and min.insync.replicas Explained

In this chapter

Wait until the copies have it

What breaks

With acks=1 the leader says “saved”, then dies before copying. The new leader never had the payment.

Three ways to respond

• More brokers, keep acks=1: The leader still acks before copying.
• acks=all + min.insync.replicas: Ack only when the in-sync copies have it. (the fix)
• acks=0 for speed: Doesn’t even wait for the leader.

The fix: acks=all + min.insync.replicas

acks=all waits for every in-sync replica. min.insync.replicas sets the floor; below it the producer gets an error instead of silent loss.

Remember: acks=all + min ISR = no silent loss.

More on Reliability problems

• Transactional Outbox Pattern with Kafka Explained
• Idempotent Kafka Consumers: Handle Duplicate Events
• Kafka Outbox Duplicates: Dedupe by Event ID, Not Offset

Keep learning

• Previous: Transactional Outbox Pattern with Kafka Explained
• Next: Idempotent Kafka Consumers: Handle Duplicate Events
• All Kafka tutorial chapters

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