> For the complete documentation index, see [llms.txt](https://docs.natsclub.cn/cn/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.natsclub.cn/cn/nats-gai-nian/core-nats/queue/queues_walkthrough.md).

# 队列 演练

NATS supports a form of load balancing using [queue groups](/cn/nats-gai-nian/core-nats/queue.md). Subscribers register a queue group name. A single subscriber in the group is randomly selected to receive the message.

## Walkthrough prerequisites

If you have not already done so, you need to [install](/cn/nats-gai-nian/what-is-nats/walkthrough_setup.md) the `nats` CLI Tool and optionally the nats-server on your machine.

### 1. Start the first member of the queue group

The `nats reply` instances don't just subscribe to the subject but also automatically join a queue group (`"NATS-RPLY-22"` by default)

```bash
nats reply foo "service instance A Reply# {{Count}}"
```

### 2. Start a second member of the queue-group

In a new window

```bash
nats reply foo "service instance B Reply# {{Count}}"
```

### 3. Start a third member of the queue-group

In a new window

```bash
nats reply foo "service instance C Reply# {{Count}}"
```

### 4. Publish a NATS message

```bash
nats request foo "Simple request"
```

### 5. Verify message publication and receipt

You should see that only one of the my-queue group subscribers receives the message and replies it, and you can also see which one of the available queue-group subscribers processed the request from the reply message received (i.e. service instance A, B or C)

### 6. Publish another message

```bash
nats request foo "Another simple request"
```

You should see that a different queue group subscriber receives the message this time, chosen at random among the 3 queue group members.

You can also send any number of requests back-to-back. From the received messages, you'll see the distribution of those requests amongst the members of the queue-group. For example: `nats request foo --count 10 "Request {{Count}}"`

### 7. Stop/start queue-group members

You can at any time start yet another service instance, or kill one and see how the queue-group automatically takes care of adding/removing those instances from the group.

## See Also

Queue groups using the NATS CLI

{% embed url="<https://youtu.be/jLTVhP08Tq0?t=101>" %}
Queue Groups NATS CLI
{% endembed %}