RabbitMQ -- part5 [Topic]

Topic exchange

上节介绍了通过使用direct exchange，将消息推送到binding的队列，但是有局限性，例如在收取日志时，想收取error级别的log，不收取info级别的log等，此时需要使用topic exchange。
topic exchange中routing_key的值是一列通过点(dots)符号分隔的单词，例如："stock.usd.nyse"，"nyse.vmw"，"quick.orange.rabbit" 可以由多个单词组成，长度上限是255字节。

topic exchange允许使用通配符：

1. *(star) 替代一个单词
2. #(hash) 替代零个或多个单词

如图：

以上图为例，创建三个bindings：Q1绑定 "*.orange.*"，表示接受有关orange相关的消息；Q2绑定 "*.*.rabbit" 和 "lazy.#"，表示接受有关rabbits和lazy相关的消息。

routing key举例：

• 消息 "quick.orange.rabbit" 将会同时被推送到两个队列中
• 消息 "lazy.orange.elephant" 也会被推送到两个队列中
• 消息 "quick.orange.fox" 会推送到Q1
• 消息 "lazy.brown.fox" 会推送到Q2
• 消息 "lazy.pink.rabbit" 会推送到Q2，虽然匹配到两个规则，但也只推送一次
• 消息 "quick.brown.fox" 将会被丢弃，因为没有匹配到任何规则
• 消息 "orange" 或 "quick.orange.male.rabbit" 没有匹配项，会被丢弃
• 消息 "lazy.orange.male.rabbit" 匹配到 "lazy.#" 规则，将会推送到Q2

如果队列的 binding key 为 "#"，则会像 fanout exchange一样，接收所有消息；如果 binding key 中没有指定 "*"(star)和 "#"(hash)，则会向 direct exchange一样。

实例代码

• 编辑 emit_log_topic.py 提交日志

#!/usr/bin/env python3
# coding=utf-8

import pika
import sys

message = ' '.join(sys.argv[1:]) or 'Hello World!'
severity = sys.argv[1] if len(sys.argv) > 2 else 'anonymouse.info'

connection = pika.BlockingConnection(pika.ConnectionParameters("localhost"))
channel = connection.channel()

# 声明使用 exchange type 为 topic
channel.exchange_declare(exchange='topic_logs', exchange_type='topic')

channel.basic_publish(exchange='topic_logs',
                      routing_key=severity,
                      body=message,
)

print("[x] Sent '%s'" % message)

connection.close()

• 编辑 receive_logs_topic.py 接收日志

#!/usr/bin/env python3
# coding=utf-8

import pika
import sys

connection = pika.BlockingConnection(pika.ConnectionParameters("localhost"))
channel = connection.channel()

# 声明 topic type
channel.exchange_declare(exchange="topic_logs", exchange_type="topic")

result = channel.queue_declare(exclusive=True)

queue_name = result.method.queue

severities = sys.argv[1:]

if not severities:
    sys.stderr.write("Usage: %s [binding_key]...\n" % sys.argv[0])
    sys.exit(1)

def callback(ch, method, properties, body):
    print('[x] Received %r' % body)

for severity in severities:
    channel.queue_bind(exchange='topic_logs',
                      queue=queue_name,
                      routing_key=severity)

channel.basic_consume(callback, queue=queue_name, no_ack=True)

print('[*] Waiting for messgaes. To exit press CTRL+C')

channel.start_consuming()

• 执行

1. 启动emit_log_topic.py

./emit_log_topic.py "kern.critical" "A critical kernel error"

2. 启动consumer1：

./receive_logs_topic.py "#"
[*] Waiting for messgaes. To exit press CTRL+C
[x] Received b'kern.critical A critical kernel error'

3. 启动consumer2：

./receive_logs_topic.py "kern.*"
[*] Waiting for messgaes. To exit press CTRL+C
[x] Received b'kern.critical A critical kernel error'

4. 启动soncumer3：

/receive_logs_topic.py "*.critical"
[*] Waiting for messgaes. To exit press CTRL+C
[x] Received b'kern.critical A critical kernel error'

5. 启动consumer4：

./receive_logs_topic.py "kern.*" "*.critical"
[*] Waiting for messgaes. To exit press CTRL+C
[x] Received b'kern.critical A critical kernel error'

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参考文档： http://www.rabbitmq.com/tutorials/tutorial-five-python.html

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