Consumer groups distribute partition load — each partition consumed by exactly one member per group.
Consumer Groups
A consumer group allows multiple consumers to share the work of reading a topic. Each partition is read by exactly one consumer in the group.
# View consumer groups
kafka-consumer-groups.sh --bootstrap-server localhost:9092 --list
# Describe group (see lag)
kafka-consumer-groups.sh --bootstrap-server localhost:9092 --group order-processor --describe
# Reset offsets (re-process from beginning)
kafka-consumer-groups.sh --bootstrap-server localhost:9092 --group order-processor --topic orders --reset-offsets --to-earliest --execute
# Key rules:
# consumers in group <= partitions (extra consumers are idle)
# each partition consumed by exactly ONE consumer per group
# different groups can read same topic independently