Module Review: Reliability

[!NOTE] This module explores the core principles of Module Review: Reliability, deriving solutions from first principles and hardware constraints to build world-class, production-ready expertise.

1. Key Takeaways

  1. Replication & ISR: Durability comes from redundancy. Only In-Sync Replicas (ISR) are eligible to become leaders.
  2. Leader Election: The Controller manages failover. Leader Epochs prevent “Split Brain” scenarios where two brokers think they are the leader.
  3. Idempotence: Prevents duplicates during retries using PID and Sequence Numbers. Enabled by default in modern Kafka.
  4. Transactions: Enables Atomic Writes across multiple partitions. Consumers must use isolation.level=read_committed.
  5. Quotas: Protects the cluster from “Noisy Neighbors” by throttling bandwidth and request rates.

2. Interactive Flashcards

Test your knowledge by clicking on the cards to flip them.

What does acks=all mean?

The Producer waits for the Leader AND all In-Sync Replicas (ISR) to acknowledge the write. This guarantees the highest durability.

What is a Split Brain?

A scenario where two brokers both believe they are the Leader for the same partition. Kafka solves this using Leader Epochs.

What prevents duplicate messages?

The Idempotent Producer, which assigns a PID and Sequence Number to every message so the broker can identify and drop duplicates.

What isolation level is needed for Transactions?

isolation.level=read_committed. Without this, consumers will see aborted transactions and uncommitted data.

3. Reliability Cheat Sheet

Feature Config Setting Benefit Trade-off
Max Durability acks=all, min.insync.replicas=2, replication.factor=3 Zero data loss guaranteed. Higher latency on produce.
Idempotence enable.idempotence=true Exactly-one write per partition. No duplicates. Slightly more metadata overhead.
Transactions transactional.id=..., isolation.level=read_committed Atomic writes across partitions. Higher latency (waiting for markers).
Quotas producer_byte_rate=... Protects cluster health. Clients get throttled (slowed down).

4. Next Steps

You’ve mastered the internal mechanics of Kafka’s reliability. Now it’s time to connect Kafka to the outside world.

Module 06: Connect & Schema Registry →