Consumer Groups

An order event may need to update a report and trigger a customer notification. Both applications need the event. If reporting becomes busy, several copies of the reporting service should help process its workload without each repeating every update.

Consumer groups support both needs: sharing work among instances of one application and letting separate applications read the same records independently. We’ll use reporting and notifications to explain group identity, partition ownership, scaling, and recovery.

The examples use ordinary consumer groups with the Apache Kafka Java client and tools version 4.3.1. Consumers subscribe to topics and poll for records. Kafka’s share groups use a different work-sharing model and are outside this chapter’s scope.