Building Data Streaming Applications with Apache Kafka

Message consumers

The consumer is any one who subscribes for topics in Kafka. Each consumer belongs to a consumer group and some consumer groups contains multiple consumers. Consumers are an interesting part of Kafka and we will cover them in detail.

Two consumers from the same group cannot consume message from a similar partition because it will lead to the message being consumed out of order. However, consumers from the same group can consume message from a different partition of the same topic simultaneously. Similarly, consumers from a different group can consume messages from the same partition in parallel without affecting the order of consumption.

So, it's clear that groups play an important role; in Kafka's initial version, Zookeeper ...