Consumer group.
also: consumer groupsA set of consumers sharing a topic: each group gets every message, and within a group each partition goes to one consumer.
the two-minute refresher
- Fan-out ACROSS groups (billing and analytics each see everything), load balancing WITHIN a group.
- One partition → one consumer per group, so per-partition order holds.
- More consumers than partitions leaves some idle: partitions cap parallelism.
- Each group tracks its own offsets, so it can replay independently.