Kafka Only One Consumer in Consumer Group Getting Messages

Question

In my setup, I have a consumer group with three processes (3 instances of a service) that can consume from Kafka. What I've found to be happing is that the first node is receiving all of the traffic. If one node is manually killed, the next node picks up all Kafka traffic, but the last remaining node sits idle.

The behavior desired is that all messages get distributed evenly across all instances within the consumer group, which is what I thought should happen. As I understand, the way Kafka works is that it is supposed to distribute the messages evenly amongst all members of a consumer group. Is my understanding correct? I've been trying to determine why it may be that only one member of the consumer group is getting all traffic with no luck. Any thoughts/suggestions?

Answer 1

You need to make sure that the topic has more than one partition to be able to consume it in parallel. A consumer in a consumer group gets one or more allocated partitions from the broker but a single partition will never be shared across several consumers within the same group unless a consumer goes offline. The number of partitions a topic has equals the maximum number of consumers in a consumer group that can feed from a topic.