Queue Groups in NATS: Load Balancing for Subscribers

Use Case Examples

• Email Sending Service
  • Subject: email.send
  • Queue group: mailers
  • Multiple worker instances subscribe to mailers. Each email task goes to one worker only.
• Payment Processing
  • Subject: payments.completed
  • Queue group: payment-workers
  • NATS distributes payment events across a pool of workers for faster throughput.
• IoT Device Commands
  • Subject: devices.cmd
  • Queue group: device-controllers
  • Only one controller handles a device command at a time.

Queue Groups vs Kafka Consumer Groups

If you’ve worked with Kafka before, Queue Groups in NATS will feel familiar. Both concepts aim to distribute messages across multiple consumers. But there are some important differences:

Aspect	NATS Queue Groups	Kafka Consumer Groups
Setup	Very lightweight, no extra configuration	Heavier setup, needs brokers and Zookeeper/Kraft
Delivery	Messages go to exactly one subscriber in the group	Each partition is assigned to exactly one consumer in the group
Persistence	Ephemeral (messages not stored) unless combined with JetStream	Persistent by default, stored on disk
Scaling	Add or remove workers anytime, messages are load balanced automatically	Scaling tied to number of partitions; can’t have more active consumers than partitions
Use Case	Real-time load balancing of tasks and jobs	Durable processing of event streams with ordered partitions

Example Perspective

• NATS Queue Group:
  Imagine an email sending service. Publishers push email tasks to email.send. Multiple workers in the mailers group share the load. If a worker is down, others pick up the tasks.
• Kafka Consumer Group:
  Imagine a stream of e-commerce orders. The topic has 6 partitions. A consumer group with 6 members can process them in parallel, each consumer handling one partition. Messages are stored on disk and can be replayed later.

Final Thoughts

Queue Groups in NATS give you simple yet powerful load balancing. They work naturally with subjects, and you don’t need to configure anything complex. Just join workers under the same group name, and NATS does the rest.