In Kafka, a consumer group is a group of one or more consumers that work together to consume messages from one or more Kafka topics. When a consumer group is created, each consumer within the group is assigned to one or more partitions within the topic, and each partition is assigned to only one consumer within the group.
Consumer groups are used to scale the consumption of messages from a topic. By using multiple consumers in a group, Kafka allows for greater parallelism and throughput, as multiple consumers can work on different partitions of a topic at the same time.
Each consumer within a group maintains its own offset, which is the position within a partition where it has last consumed messages. This allows each consumer to consume messages independently and at its own pace, while still ensuring that each message is consumed by only one consumer within the group.
Kafka provides a mechanism for rebalancing consumer groups when new consumers are added or existing consumers are removed from the group. When a rebalance occurs, the partitions assigned to each consumer within the group are redistributed to ensure that each partition is assigned to only one consumer within the group.
Overall, consumer groups are a key component of Kafka’s scalability and allow for efficient and parallel consumption of messages from one or more Kafka topics.