RabbitMQ 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：

1. channel.queue_bind(exchange=exchange_name,
2. queue=queue_name)

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 :

1. channel.queue_bind(exchange=exchange_name,
2. queue=queue_name,
3. routing_key='black')

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：

1. channel.exchange_declare(exchange='direct_logs',
2. type='direct')

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：

1. channel.basic_publish(exchange='direct_logs',
2. routing_key=severity,
3. body=message)

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：

1. result = channel.queue_declare(exclusive=True)
2. queue_name = result.method.queue
3. for severity in severities:
4. channel.queue_bind(exchange='direct_logs',
5. queue=queue_name,
6. routing_key=severity)

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:

1. #!/usr/bin/env python
2. import pika
3. import sys
4. connection = pika.BlockingConnection(pika.ConnectionParameters(
5. host='localhost'))
6. channel = connection.channel()
7. channel.exchange_declare(exchange='direct_logs',
8. type='direct')
9. severity = sys.argv[1] if len(sys.argv) > 1 else 'info'
10. message = ' '.join(sys.argv[2:]) or 'Hello World!'
11. channel.basic_publish(exchange='direct_logs',
12. routing_key=severity,
13. body=message)
14. print " [x] Sent %r:%r" % (severity, message)
15. connection.close()

#!/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[1] if len(sys.argv) > 1 else 'info'
message = ' '.join(sys.argv[2:]) or 'Hello World!'
channel.basic_publish(exchange='direct_logs',
                      routing_key=severity,
                      body=message)
print " [x] Sent %r:%r" % (severity, message)
connection.close()

The code for receive_logs_direct.py:

1. #!/usr/bin/env python
2. import pika
3. import sys
4. connection = pika.BlockingConnection(pika.ConnectionParameters(
5. host='localhost'))
6. channel = connection.channel()
7. channel.exchange_declare(exchange='direct_logs',
8. type='direct')
9. result = channel.queue_declare(exclusive=True)
10. queue_name = result.method.queue
11. severities = sys.argv[1:]
12. if not severities:
13. print >> sys.stderr, "Usage: %s [info] [warning] [error]" % \
14. (sys.argv[0],)
15. sys.exit(1)
16. for severity in severities:
17. channel.queue_bind(exchange='direct_logs',
18. queue=queue_name,
19. routing_key=severity)
20. print ' [*] Waiting for logs. To exit press CTRL+C'
21. def callback(ch, method, properties, body):
22. print " [x] %r:%r" % (method.routing_key, body,)
23. channel.basic_consume(callback,
24. queue=queue_name,
25. no_ack=True)
26. channel.start_consuming()

#!/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[1:]
if not severities:
    print >> sys.stderr, "Usage: %s [info] [warning] [error]" % \
                         (sys.argv[0],)
    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 " [x] %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：

1. $ python receive_logs_direct.py warning error > logs_from_rabbit.log

$ python receive_logs_direct.py warning error > logs_from_rabbit.log

打印所有log到屏幕：

1. $ python receive_logs_direct.py info warning error
2. [*] Waiting for logs. To exit press CTRL+C

$ python receive_logs_direct.py info warning error
 [*] Waiting for logs. To exit press CTRL+C

转载自： anzhsoft: http://blog.csdn.net/anzhsoft/article/details/19630147

参考资料：

1. http://www.rabbitmq.com/tutorials/tutorial-four-python.html

 

阅读全文