Group coordinator

As explained in Apache Kafka in Action

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

A group coordinator is the Kafka broker responsible for managing one consumer group's membership and coordination. Kafka distributes coordinator responsibility across brokers according to group ID, avoiding a single coordination bottleneck. section 9.4.1

A consumer contacts the coordinator through this sequence:

• Send FindCoordinator to any broker to discover the coordinator's host and port. section 9.4.1
• Send JoinGroup to join or rejoin and initiate synchronization; the request waits until potential members report. section 9.4.1
• Send Heartbeat signals to indicate that the consumer remains active, and use SyncGroup during group management. section 9.4.1

Figure 9.4 The Kafka Rebalance Protocol allows a group to distribute certain resources among its members, for example, consumer partitions. In this process, a broker acts as the group coordinator, and one of the consumers serves as the group leader.

Shows how the coordinator and a consumer acting as group leader participate in distributing partitions during a rebalance. section 9.4.1

How Apache Kafka in Action covers it

How deep it goes

Explains coordinator discovery, joining, heartbeats, and synchronization, but does not detail assignment algorithms.

Examples

Uses FindCoordinator, JoinGroup, Heartbeat, and SyncGroup requests plus a rebalance diagram.

What you can do after

Understand how consumers locate their coordinator and communicate during membership and rebalance operations.

How it connects

Connects consumer groups, Kafka brokers, consumer-group rebalancing, partitions, and the group leader.

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Also explained in

• 

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

  liveBookmanning.com
  Kafka Streams in Action, Second EditionA group coordinator is the Kafka broker responsible for managing a consumer group's membership, rebalancing, and committed offsets.

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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 Apache Kafka in Action. The section links point to the parts of the book it draws on.