Group coordinator

As explained in Kafka Streams in Action, Second Edition

A group coordinator is the Kafka broker responsible for managing a consumer group's membership, rebalancing, and committed offsets.

A group coordinator is a Kafka broker responsible for tracking membership for a subset of consumer groups. It receives join requests and detects members that miss polling or heartbeat timeouts. section 4.3.2

When membership changes, the coordinator triggers a rebalance. Consumers rejoin, and topic partitions move between members so processing can continue after joins or failures. section 4.3.2

The coordinator’s role becomes visible when:

• A new consumer joins and receives partitions taken from existing members. section 4.3.2
• A consumer stops communicating within the configured timeout and its partitions move to active members. section 4.3.2
• An eager rebalance pauses processing broadly, while cooperative rebalancing limits disruption to partitions marked for reassignment. section 4.3.2

Figure 4.12 Group coordinator is a broker assigned to track a subset of consumer groups, and the group leader is a consumer communicating with the group coordinator.

Use the diagram to distinguish the broker-side group coordinator from the consumer-side group leader and their communication. section 4.3.2

How Kafka Streams in Action, Second Edition covers it

How deep it goes

Explains membership detection, timeout-driven rebalancing, partition movement, and eager versus cooperative protocols.

Examples

Uses new-member joins, failed consumers, heartbeat timeouts, and diagrams of eager and cooperative partition reassignment.

What you can do after

Diagnose why consumer-group membership changes trigger partition reassignment and processing pauses.

How it connects

Connects consumer groups with heartbeats, session timeouts, rebalancing, group leaders, and topic partitions.

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Also explained in

• 

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  Kafka for ArchitectsA group coordinator is the Kafka broker responsible for managing a consumer group and coordinating its membership and partition assignments.
• 

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  Apache Kafka in ActionA group coordinator is the Kafka broker responsible for managing a specific consumer group's membership, liveness, and assignments.

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Related concepts

• consumer group rebalancingproduces · Consumer group rebalancing is the redistribution of topic-partition assignments among consumer group members after membership or partition availability changes.
• Kafka brokerkind of · A Kafka broker is a server process in an Apache Kafka cluster that stores records and handles producer, consumer, and other client requests.
• message brokerkind of · A message broker is intermediary software that receives, routes, and delivers messages between communicating producers and consumers.
• Kafka producerused by · A Kafka producer is an application or client that publishes records to Kafka topics.
• group leaderused by · A group leader is the elected Kafka consumer-group member responsible for calculating the group’s partition assignments.

This explainer was generated by Manning's knowledge graph from the text of Kafka Streams in Action, Second Edition. The section links point to the parts of the book it draws on.