Majority

As explained in Apache Kafka in Action

A majority is more than half of the members of a group, sufficient for quorum-based agreement in a distributed system.

A majority is more than half of a group. In a Kafka coordination cluster, it is the minimum needed to keep quorum-based agreement operating after failures. section 16.1.4

Two versus three data centers

With three coordination nodes spread across only two data centers, one data center may contain the majority. Losing that location can remove the majority and stop the Kafka cluster. Distributing the nodes across at least three data centers reduces this risk. section 16.1.4

Figure 16.2 In a stretched cluster, our Kafka brokers are distributed among multiple data centers.

Use the stretched-cluster figure to see how Kafka brokers and coordination nodes are distributed across data centers. section 16.1.4

How Apache Kafka in Action covers it

How deep it goes

Explains majority through data-center placement and three-node failure scenarios, without deriving quorum mathematics.

Examples

Contrasts two- and three-data-center layouts, including three coordination nodes and a two-out-of-three failure.

What you can do after

Operate/configure stretched Kafka clusters so coordination nodes retain a majority after a data-center failure.

How it connects

Connects majority with quorum, Kafka clusters, coordination nodes, ZooKeeper, KRaft, and data-center failures.

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Related concepts

• quorumincludes · A quorum is the minimum number or proportion of distributed participants whose responses or agreement are sufficient for an operation or decision.

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.