Explain Kafka topics, partitions, brokers, and message ordering

Explain Kafka's core building blocks and its ordering guarantees.

• Topic: a named, logical stream of records that producers write to and consumers read from.
• Partition: an ordered, append-only shard of a topic. Partitions are the unit of parallelism and each lives on a broker (with replicas for fault tolerance).
• Broker: a Kafka server that hosts partitions, serves reads/writes, and participates in replication; one partition replica is the leader, others are followers (the ISR set).
• Message ordering: guaranteed only within a partition, not across a topic. To keep related events ordered, give them the same key so they hash to the same partition.

Follow-ups usually cover consumer groups, how partition count bounds consumer parallelism, and replication/failover.