What is a Kafka Broker?

A Kafka Broker is a Kafka server — a node in the Kafka cluster. It stores messages in topic partitions on disk, serves producer writes and consumer reads, and replicates data to other brokers. Each broker in a cluster has a unique broker.id. Key responsibilities: Partition leadership: each partition has one broker as the leader (handles all reads and writes) and others as followers (replicate data). Message storage: messages are stored in segment files on disk, organized by topic and partition. Client coordination: brokers provide metadata (which broker is the leader for each partition) to clients. A typical production cluster has 3–12 brokers. One broker acts as the Controller (elected leader among brokers) responsible for partition leader elections and cluster metadata.