rabbitmq3.7.3 发布了一个新的 exchange x-random

direct exchange 同一个 routing key 可以绑定多个 queue，当给这个routing key发消息时，所有 queue 都会投递。这个行为对于一些场景不适用，有时我们希望只有一个 queue 收到消息。x-random 就是解决这个问题的。

这个 exchange 之前是第三方实现的，现在在官方给的 3.7.3（2018-01-30发布） 已经自带了，但仍需要人工激活。升级 rabbitmq-server 后手工执行：

rabbitmq-plugins enable rabbitmq_random_exchange

激活后在 web console 就可以看到这种 exchange 了：

测试：

import asyncio
import traceback

import asynqp

async def test(case_id):

    def listen(id):
        def callback(msg):
            print('[{}] [{}] Received: {}'.format(case_id, id, msg.body))
            msg.ack()
        return callback

    try:
        connection = await asynqp.connect('localhost', 5672, username='guest', password='guest')
        channel = await connection.open_channel()
        exchange = await channel.declare_exchange('rnd.exchange', 'x-random')

        for i in range(0,10):
            queue = await channel.declare_queue('test.queue_%s' % i)
            await queue.bind(exchange, 'routing.key')
            await queue.consume(listen(i))

        async def send_msg():
            for i in range(0, 50):
                msg = asynqp.Message({'hello': '%s world %s, random exchange'%(case_id, i)})
                exchange.publish(msg, 'test.queue')
                await asyncio.sleep(1)

        asyncio.ensure_future(send_msg())

    except Exception as ex:
        traceback.print_exc()

if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(asyncio.wait([test('A'), asyncio.sleep(10)]))

效果：

[A] [5] Received: b'{"hello": "A world 0, random exchange"}'
[A] [6] Received: b'{"hello": "A world 1, random exchange"}'
[A] [1] Received: b'{"hello": "A world 2, random exchange"}'
[A] [8] Received: b'{"hello": "A world 3, random exchange"}'
[A] [3] Received: b'{"hello": "A world 4, random exchange"}'
[A] [4] Received: b'{"hello": "A world 5, random exchange"}'
[A] [6] Received: b'{"hello": "A world 6, random exchange"}'
[A] [8] Received: b'{"hello": "A world 7, random exchange"}'
[A] [5] Received: b'{"hello": "A world 8, random exchange"}'
[A] [2] Received: b'{"hello": "A world 9, random exchange"}'

可见消息会投递到随机选择的某个 queue。

random-exchange 的代码：https://github.com/rabbitmq/rabbitmq-random-exchange

注意：publish 提供的 routing key 并没有处理，不论提供什么 routing key  都会对所有绑定到该 exchange 的 queue 推送消息，所以效果相当于 fanout + random。不实用。

这个