Coordinator manages all consumer modules, making sure they are configured, started, and stopped at the appropriate time.

KafkaClient is a consumer module which connects to a single Apache Kafka cluster and reads consumer group information from the offsets topic in the cluster, which is typically __consumer_offsets.

KafkaZkClient is a consumer module which connects to the Zookeeper ensemble where an Apache Kafka cluster maintains metadata, and reads consumer group information from the /consumers tree (older ZK-based consumers).