What is rebalancing in Kafka? Why can it occur without changing the infrastructure?

Rebalancing in Kafka is the process of redistributing partitions among consumers within a consumer group. It occurs when the group composition changes (for example, when a consumer is added or removed), or when subscriptions to topics change.

Rebalancing can happen without infrastructure changes, for instance, if a consumer crashes or stops responding, or if consumers dynamically connect and disconnect. In this case, Kafka redistributes partitions among the remaining active consumers to ensure load balancing and guarantee that each partition is processed by exactly one consumer.

Thus, rebalancing is a mechanism to ensure the resilience and scalability of message consumption without requiring changes to the Kafka broker infrastructure.