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Apache Kafka

Production-grade notes on Apache Kafka — the log format on disk, the durability contract, the partition strategy that decides whether your cluster scales or melts, and the operational gotchas that only show up under real load.

7 articles · updated regularly

Jul 06, 20269 min

The Order That Shipped Twice: A Rebalance in the Middle of a Long Batch

A Kafka consumer processed every message exactly once for months, and then one afternoon a handful of orders shipped twice. Nothing had crashed, no message was redelivered by a broker retry, and the offsets on the dashboard looked healthy. The consumer had committed an offset it had not actually finished processing, a rebalance handed the same partition to another instance, and that instance dutifully reprocessed a batch the first one was still working through.

KafkaConsumers

Nov 04, 202514 min

The Night Kafka Ate Itself: A 6-Hour Outage Postmortem

A real outage, hour by hour. Three brokers, one bad config, six hours of pain, and the seven-line fix that should have been there from day one.

KafkaPostmortem

Oct 24, 20259 min

Kafka Streams vs Flink vs Plain Consumer: Choosing the Right Layer

Three legitimate ways to process a Kafka topic — which one fits your shape of problem.

KafkaStreaming

Oct 02, 20257 min

Partitioning Strategy: Keys, Hot Partitions, and Ordering

Ordering guarantees in Kafka are per-partition. Getting the key right is the whole game.

KafkaDesign

Sep 18, 20258 min

Consumer Group Rebalancing: Eager, Cooperative, and Static

Why your consumer hangs for 30s every deploy — and how cooperative rebalance + static membership fixes it.

KafkaOperations

Aug 28, 202511 min

Exactly-Once Semantics in Kafka: Idempotence & Transactions

How producer IDs, sequence numbers, and the transaction coordinator combine to give you exactly-once — and when they don't.

KafkaReliability

Aug 11, 20259 min

Kafka Internals: Log Segments, Offsets & The Commit Protocol

A tour of how Kafka persists records — segment files, index files, high watermark, and the acks=all contract.

KafkaArchitecture

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