Kafka Consumer Group Assignment

Kevin Feasel



David Brinegar discusses how consumers within an Apache Kafka consumer group get assigned work:

Or one might want some assignment that results in uniform workloads, based on the number of messages in each partition.  But until we have pluggable assignment functions, the reference implementation has a straightforward assignment strategy called Range Assignment.  There is also a newer Round Robin assignor which is useful for applications like Mirror Maker, but most applications just use the default assignment algorithm.

The Range Assignor tries to land on a uniform distribution of partitions, at least within each topic, while at the same time avoiding the need to coordinate and bargain between nodes.  This last goal, independent assignment, is done by each node executing a fixed algorithm:  sort the partitions, sort the consumers, then for each topic take same-sized ranges of partitions for each consumer.  Where the sizes cannot be the same, the consumers at the beginning of the sorted list will end up with one extra partition.  With this algorithm, each application node can see the entire layout by itself, and from there take up the right assignments.

Click through to see an example of how this is implemented.

Related Posts

Enabling Exactly-Once Kafka Streams

Guozhang Wang wraps up his exactly-once series in Kafka: When restarting the application from the point of failure, we would then try to resume processing from the previously remembered position in the input Kafka topic, i.e. the committed offset. However, since the application was not able to commit the offset of the processed message A before crashing […]

Read More

Avro Schemas In Kafka

Stephane Maarek explains the value of using Apache Avro as a schema structure for your Kafka topics: Avro has support for primitive types ( int, string, long, bytes, etc…), complex types (enum, arrays, unions, optionals), logical types (dates, timestamp-millis, decimal), and data record (name and namespace). All the types you’ll ever need. Avro has support for embedded documentation. Although documentation is optional, in my workflow I […]

Read More


October 2016
« Sep Nov »