RabbitMQ消息队列（五）：Routing 消息路由
上篇文章中，我们构建了一个简单的日志系统。接下来，我们将丰富它：能够使用不同的severity来监听不同等级的log。比如我们希望只有error的log才保存到磁盘上。1. Bindings绑定
上篇文章中我们是这么做的绑定：
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[*]channel.queue_bind(exchange=exchange_name,
[*] queue=queue_name)
绑定其实就是关联了exchange和queue。或者这么说：queue对exchagne的内容感兴趣，exchange要把它的Message deliver到queue中。
实际上，绑定可以带routing_key 这个参数。其实这个参数的名称和basic_publish 的参数名是相同了。为了避免混淆，我们把它成为binding key。
使用一个key来创建binding :
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[*]channel.queue_bind(exchange=exchange_name,
[*] queue=queue_name,
[*] routing_key='black')
对于fanout的exchange来说，这个参数是被忽略的。
2. Direct exchange
Direct exchange的路由算法非常简单：通过binding key的完全匹配，可以通过下图来说明。
exchange X和两个queue绑定在一起。Q1的binding key是orange。Q2的binding key是black和green。
当P publish key是orange时，exchange会把它放到Q1。如果是black或者green那么就会到Q2。其余的Message都会被丢弃。
3. Multiple bindings
多个queue绑定同一个key是可以的。对于下图的例子，Q1和Q2都绑定了black。也就是说，对于routing key是black的Message，会被deliver到Q1和Q2。其余的Message都会被丢弃。
4. Emitting logs
首先是我们要创建一个direct的exchange：
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[*]channel.exchange_declare(exchange='direct_logs',
[*] type='direct')
我们将使用log的severity作为routing key，这样Consumer可以针对不同severity的log进行不同的处理。
publish：
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[*]channel.basic_publish(exchange='direct_logs',
[*] routing_key=severity,
[*] body=message)
我们使用三种severity：'info', 'warning', 'error'.
5. Subscribing
对于queue，我们需要绑定severity：
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[*]result = channel.queue_declare(exclusive=True)
[*]queue_name = result.method.queue
[*]
[*]for severity in severities:
[*] channel.queue_bind(exchange='direct_logs',
[*] queue=queue_name,
[*] routing_key=severity)
6. 最终版本
The code for emit_log_direct.py:
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[*]#!/usr/bin/env python
[*]import pika
[*]import sys
[*]
[*]connection = pika.BlockingConnection(pika.ConnectionParameters(
[*] host='localhost'))
[*]channel = connection.channel()
[*]
[*]channel.exchange_declare(exchange='direct_logs',
[*] type='direct')
[*]
[*]severity = sys.argv if len(sys.argv) > 1 else 'info'
[*]message = ' '.join(sys.argv) or 'Hello World!'
[*]channel.basic_publish(exchange='direct_logs',
[*] routing_key=severity,
[*] body=message)
[*]print " Sent %r:%r" % (severity, message)
[*]connection.close()
The code for receive_logs_direct.py:
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[*]#!/usr/bin/env python
[*]import pika
[*]import sys
[*]
[*]connection = pika.BlockingConnection(pika.ConnectionParameters(
[*] host='localhost'))
[*]channel = connection.channel()
[*]
[*]channel.exchange_declare(exchange='direct_logs',
[*] type='direct')
[*]
[*]result = channel.queue_declare(exclusive=True)
[*]queue_name = result.method.queue
[*]
[*]severities = sys.argv
[*]if not severities:
[*] print >> sys.stderr, "Usage: %s " % \
[*] (sys.argv,)
[*] sys.exit(1)
[*]
[*]for severity in severities:
[*] channel.queue_bind(exchange='direct_logs',
[*] queue=queue_name,
[*] routing_key=severity)
[*]
[*]print '
[*] Waiting for logs. To exit press CTRL+C'
[*]
[*]def callback(ch, method, properties, body):
[*] print " %r:%r" % (method.routing_key, body,)
[*]
[*]channel.basic_consume(callback,
[*] queue=queue_name,
[*] no_ack=True)
[*]
[*]channel.start_consuming()
我们想把warning和error的log记录到一个文件中：
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[*]$ python receive_logs_direct.py warning error > logs_from_rabbit.log
打印所有log到屏幕：
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[*]$ python receive_logs_direct.py info warning error
[*]
[*] Waiting for logs. To exit press CTRL+C
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