Consumer group
A consumer group is a logical set of message consumers that cooperatively processes a shared stream by distributing its partitions among group members.
Kafka for Architects
A shared consumer group is a Kafka consumption mode that permits multiple consumers in a group to receive records from the same partition.
- How it is used
- Coordinates parallel consumption within a group while allowing other groups to read the same topic independently.
- How deep it goes
- Explains classic partition assignment, group offsets, lag, and rebalances; identifies shared groups without detailing their mechanics.
- Examples
- Uses customer-data consumers, balance updates, and partition-assignment diagrams to illustrate collaboration and ordering.
- What you can do after
- Operate/configure Kafka consumers with group.id and use partition count and lag to assess scaling.
Apache Kafka in Action
A consumer group is a set of consumers that collaboratively consume topic partitions, with each partition assigned to one consumer in the group.
- How it is used
- Scales a service’s consumption while letting other services read the same topic independently.
- How deep it goes
- Explains group IDs, whole-partition assignment, stored offsets, coordination, rebalance triggers, and assignment options without detailing the protocol’s steps.
- Examples
- Demonstrates a console consumer restarting with saved progress and two consumers splitting price-change records by partition.
- What you can do after
- Operate/configure it by setting a group ID, adding consumer instances, and recognizing partition-level scaling and rebalance trade-offs.
Kafka Streams in Action, Second Edition
A consumer group is a set of Kafka consumers that jointly consume a topic's partitions, with each partition assigned to at most one group member at a time.
- How it is used
- Coordinates multiple Kafka consumers as one logical consumer for parallel topic-partition processing.
- How deep it goes
- Explains group membership, partition assignment, failure-triggered rebalancing, polling timeouts, heartbeats, and coordinator roles.
- Examples
- Uses six partitions shared by three consumers, a failed consumer, and a Java KafkaConsumer polling ProductTransaction records.
- What you can do after
- Operate a Kafka consumer group by configuring group.id, subscribing, polling, and anticipating partition reassignment.
Read how Kafka Streams in Action, Second Edition explains consumer group →
Troubleshooting Java, Second Edition
A consumer group is a set of consumers that cooperatively processes the same Kafka topic stream.
- How it is used
- Uses consumer groups and offsets to investigate whether Kafka services received, skipped, or failed to process events.
- How deep it goes
- Explains cooperative processing, partition assignment, offset behavior, and configuration diagnosis, but not consumer-group implementation code.
- Examples
- Uses a missing welcome-email incident, a misconfigured topic, consumer-group offsets, and replayed UserRegistered events.
- What you can do after
- Diagnose missing Kafka events by checking consumer-group offsets and topic configuration, then validate recovery through event replay.
Read how Troubleshooting Java, Second Edition explains consumer group →
Related concepts
- group.idconfigured by · group.id is a Kafka consumer configuration property that identifies the consumer group whose partition assignments and consumption progress the consumer participates in.
- offsetuses · An offset is a position or displacement measured relative to a reference point, such as within an ordered sequence, memory region, or layout.
- partitionuses · A partition is a distinct subdivision of a larger data, storage, or work unit that can be stored, managed, or processed separately.
- Apache Kafkaused by · Apache Kafka is a distributed event-streaming platform for publishing, storing, processing, and consuming streams of records.
- publish/subscribe modelimplements · The publish-subscribe model is a messaging pattern in which publishers send messages without addressing specific recipients, and subscribers receive messages according to their interests or subscriptions.
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