Pick a partition key that keeps one customer's events in order

Two updates for the same order arrive out of order downstream, and support wants to know why.

IntermediateRead 6 minDoing: an afternoon6 steps

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What you'll have at the end

A producer keyed by the entity id, proven to always land the same id on one partition in order

Before you start

You need

A Kafka producer already publishing order events, and a downstream service that needs one customer's events, across every order they place, delivered in the order they actually happened.

Not covered

How many partitions the topic should have in the first place, a separate sizing decision this recipe assumes is already settled.

Leans on

6 steps

Where to go next

Right-size a new Kafka topic's partitions

when the count itself, not which field routes to a partition, is the open question.

Messages vanish when a Kafka producer isn't idempotent

when retries onto the correct partition, not routing to the wrong one, are what's scrambling delivery.

Checked 25 Aug 2026

Part of the Apache Kafka cookbook