A Kafka broker is a server that stores partitions and serves producers/consumers. A cluster is a group of brokers. Each partition has exactly one leader broker (handles all reads/writes) and N-1 follower brokers (replicate the leader). The controller broker manages cluster metadata — leader elections, broker registration, topic creation.
Key configuration
broker.id — unique integer per broker
num.network.threads=3 — network I/O threads
num.io.threads=8 — disk I/O threads