The purpose of Describe Kafka Topic is to know the leader for the topic, the broker instances acting as replicas for the topic, and the number of partitions of a Kafka Topic that has been created with.
For creating a Kafka Topic, refer Create a Topic in Kafka Cluster.
Consider there are three broker instances running on a local machine and to know which kafka broker is doing what with a kafka topic(say my-topic), run the following command
$ bin/kafka-topics.sh --describe --zookeeper localhost:2181 --topic my-topic
Replacemy-topic with your topic name. And also, it is assumed that you are running kafka with default configuration (zookeeper running at 2181).
$ bin/kafka-topics.sh --describe --zookeeper localhost:2181 --topic my-topic Topic:my-topic PartitionCount:1 ReplicationFactor:3 Configs: Topic: my-topic Partition: 0 Leader: 1 Replicas: 1,2,0 Isr: 1,2,0
The result explains that
Replicas: 1,2,0 meaning broker instances 0, 1 and 2 are acting as nodes that replicate the log irrespective of one being a leader.
Isr: 1,2,0 meaning broker instances 1, 2 and 0 are in-sync replicas.
PartitionCount:1 and ReplicationFactor:3 are the details used while creating the topic.
Now Kafka Producers may send messages to the Kafka topic, my-topic and Kafka Consumers may subscribe to the Kafka Topic.
In this Apache Kafka Tutorial – Describe Kafka Topic, we have learnt to check Kafka Broker Instance that is acting as leader for a Kafka Topic, and the Broker Instances acting as replicas and in-sync replicas for the Kafka Topic.