What is the role of a Kafka broker?

A Kafka broker is a server in the storage layer of the cluster: it stores partition data and handles producer and consumer requests. Each broker hosts replicas of many partitions; for each partition one replica is the leader and the others are followers. All writes go to the leader, reads can go to the leader or the followers, and followers fetch from the leader just as a normal consumer would. A cluster has multiple brokers for fault tolerance and scalability: if a server fails, the others take over its work. In KRaft mode a server is configured as a broker, a controller or both with process.roles; controllers form the metadata quorum, one is the active controller and the rest are hot standbys, and the active controller elects a new leader from the remaining in-sync replicas when it detects a broker failure.

Expected key concepts: broker, storage layer, partition data, producer, consumer, leader, followers, controller, KRaft, process.roles, metadata quorum