rabbitmq使用(三)
Publish/Subscribe
In the previous tutorial we created a work queue. The assumption behind a work queue is that each task is delivered to exactly one worker. In this part we'll do something completely different -- we'll deliver a message to multiple consumers. This pattern is known as "publish/subscribe".
To illustrate the pattern, we're going to build a simple logging system. It will consist of two programs -- the first will emit log messages and the second will receive and print them.
In our logging system every running copy of the receiver program will get the messages. That way we'll be able to run one receiver and direct the logs to disk; and at the same time we'll be able to run another receiver and see the logs on the screen.
Essentially, published log messages are going to be broadcast to all the receivers.
Exchanges
In previous parts of the tutorial we sent and received messages to and from a queue. Now it's time to introduce the full messaging model in Rabbit.
Let's quickly go over what we covered in the previous tutorials:
- A producer is a user application that sends messages.
- A queue is a buffer that stores messages.
- A consumer is a user application that receives messages.
The core idea in the messaging model in RabbitMQ is that the producer never sends any messages directly to a queue. Actually, quite often the producer doesn't even know if a message will be delivered to any queue at all.
Instead, the producer can only send messages to an exchange. An exchange is a very simple thing. On one side it receives messages from producers and the other side it pushes them to queues. The exchange must know exactly what to do with a message it receives. Should it be appended to a particular queue? Should it be appended to many queues? Or should it get discarded. The rules for that are defined by the exchange type.
There are a few exchange types available: direct, topic, headers and fanout. We'll focus on the last one -- the fanout. Let's create an exchange of that type, and call it logs:
channel.exchange_declare(exchange='logs',
type='fanout')
The fanout exchange is very simple. As you can probably guess from the name, it just broadcasts all the messages it receives to all the queues it knows. And that's exactly what we need for our logger.
Now, we can publish to our named exchange instead:
channel.basic_publish(exchange='logs',
routing_key='',
body=message)
Temporary queues
As you may remember previously we were using queues which had a specified name (remember hello and task_queue?). Being able to name a queue was crucial for us -- we needed to point the workers to the same queue. Giving a queue a name is important when you want to share the queue between producers and consumers.
But that's not the case for our logger. We want to hear about all log messages, not just a subset of them. We're also interested only in currently flowing messages not in the old ones. To solve that we need two things.
Firstly, whenever we connect to Rabbit we need a fresh, empty queue. To do it we could create a queue with a random name, or, even better - let the server choose a random queue name for us. We can do this by not supplying the queue parameter to queue_declare:
result = channel.queue_declare()
At this point result.method.queue contains a random queue name. For example it may look like amq.gen-JzTY20BRgKO-HjmUJj0wLg.
Secondly, once we disconnect the consumer the queue should be deleted. There's an exclusive flag for that:
result = channel.queue_declare(exclusive=True)
Bindings
We've already created a fanout exchange and a queue. Now we need to tell the exchange to send messages to our queue. That relationship between exchange and a queue is called abinding.
channel.queue_bind(exchange='logs',
queue=result.method.queue)
From now on the logs exchange will append messages to our queue.
Putting it all together
The producer program, which emits log messages, doesn't look much different from the previous tutorial. The most important change is that we now want to publish messages to our logs exchange instead of the nameless one. We need to supply a routing_key when sending, but its value is ignored for fanout exchanges. Here goes the code for emit_log.py script:
#!/usr/bin/env python
import pika
import sys connection = pika.BlockingConnection(pika.ConnectionParameters(
host='localhost'))
channel = connection.channel() channel.exchange_declare(exchange='logs',
type='fanout') message = ' '.join(sys.argv[1:]) or "info: Hello World!"
channel.basic_publish(exchange='logs',
routing_key='',
body=message)
print " [x] Sent %r" % (message,)
connection.close()
As you see, after establishing the connection we declared the exchange. This step is neccesary as publishing to a non-existing exchange is forbidden.
The messages will be lost if no queue is bound to the exchange yet, but that's okay for us; if no consumer is listening yet we can safely discard the message.
The code for receive_logs.py:
#!/usr/bin/env python
import pika connection = pika.BlockingConnection(pika.ConnectionParameters(
host='localhost'))
channel = connection.channel() channel.exchange_declare(exchange='logs',
type='fanout') result = channel.queue_declare(exclusive=True)
queue_name = result.method.queue channel.queue_bind(exchange='logs',
queue=queue_name) print ' [*] Waiting for logs. To exit press CTRL+C' def callback(ch, method, properties, body):
print " [x] %r" % (body,) channel.basic_consume(callback,
queue=queue_name,
no_ack=True) channel.start_consuming()
We're done. If you want to save logs to a file, just open a console and type:
$ python receive_logs.py > logs_from_rabbit.log
If you wish to see the logs on your screen, spawn a new terminal and run:
$ python receive_logs.py
And of course, to emit logs type:
$ python emit_log.py
Using rabbitmqctl list_bindings you can verify that the code actually creates bindings and queues as we want. With two receive_logs.py programs running you should see something like:
$ sudo rabbitmqctl list_bindings
Listing bindings ...
logs exchange amq.gen-JzTY20BRgKO-HjmUJj0wLg queue []
logs exchange amq.gen-vso0PVvyiRIL2WoV3i48Yg queue []
...done.
rabbitmq使用(三)的更多相关文章
- RabbitMQ(三) -- Publish/Subscribe
RabbitMQ(三) -- Publish/Subscribe `rabbitmq`支持一对多的模式,一般称为发布/订阅.也就是说,生产者产生一条消息后,`rabbitmq`会把该消息分发给所有的消 ...
- rabbitMQ第三篇:采用不同的交换机规则
在上一篇我们都是采用发送信息到队列然后队列把信息在发送到消费者,其实实际情况并非如此,rabbitMQ其实真正的思想是生产者不发送任何信息到队列,甚至不知道信息将发送到哪个队列.相反生产者只能发送信息 ...
- python使用rabbitMQ介绍三(发布订阅模式)
一.模式介绍 在前面的例子中,消息直接发送到queue中. 现在介绍的模式,消息发送到exchange中,消费者把队列绑定到exchange上. 发布-订阅模式是把消息广播到每个消费者,每个消费者接收 ...
- 【RabbitMQ】三种类型交换器 Fanout,Direct,Topic(转)
出处:https://blog.csdn.net/fxq8866/article/details/62049393 RabbitMQ服务器会根据路由键将消息从交换器路由到队列中,如何处理投递到多个队列 ...
- rabbitMQ的三种路由模式
rabbitMQ工作流程: 1.声明交换机 2.声明消息队列 3.绑定交换机和队列 4.生产者往交换机里发送新消息 5.交换机根据所选的模式和routingKey决定消息发往哪条消息队列 6.一个消费 ...
- RabbitMQ系列(三)--Java API
基于java使用RabbitMQ 框架:SpringBoot1.5.14.RELEASE maven依赖: <dependency> <groupId>com.rabbitmq ...
- RabbitMQ实战(三)-高级特性
0 相关源码 1 你将学到 如何保证消息百分百投递成功 幂等性 如何避免海量订单生成时消息的重复消费 Confirm确认消息.Return返回消息 自定义消费者 消息的ACK与重回队列 限流 TTL ...
- RabbitMQ(三):RabbitMQ与Spring Boot简单整合
RabbitMQ是目前非常热门的一款消息中间件,不管是互联网大厂还是中小企业都在大量使用.Spring Boot的兴起,极大地简化了Spring的开发,本文将使用Spring Boot与RabbitM ...
- 消息中间件——RabbitMQ(三)理解RabbitMQ核心概念和AMQP协议!
前言 本章学习,我们可以了解到以下知识点: 互联网大厂为什么选择RabbitMQ? RabbiMQ的高性能之道是如何做到的? 什么是AMQP高级协议? AMQP核心概念是什么? RabbitMQ整体架 ...
- Rabbitmq交换机三种模式介绍
1.topic 将路由键和某模式进行匹配.此时队列需要绑定要一个模式上.符号“#”匹配一个或多个词,符号“*”匹配不多不少一个词.因此“abc.#”能够匹配到“abc.def.ghi”,但是“abc. ...
随机推荐
- 【转】每天一个linux命令(1):ls命令
ls命令是linux下最常用的命令.ls命令就是list的缩写,缺省下ls用来打印出当前目录的清单.如果ls指定其他目录,那么就会显示指定目录里的文件及文件夹清单. 通过ls命令不仅可以查看linux ...
- CSS高度塌陷问题解决方案
高度塌陷的存在:原因分析 1 <!DOCTYPE html> <html> <head> <meta charset="utf-8" /& ...
- SYN flooding引发的网络故障
故障现象: 1.应用无法通过外网访问,应用服务器所在的内网网段之间(web和db数据库之间访问丢包严重)不能互相访问 其他网段正常 2.怀疑是网络设备问题,将连接该网段设备的交换机重启后故障依旧,通过 ...
- Web Services基础学习(W3C)
1.Web services 使用 XML 来编解码数据,并使用 SOAP 来传输数据 2.基础的 Web Services 平台是 XML + HTTP. Web services 平台的元素: S ...
- PYTHON-文件处理-练习
## 一.实现用户注册功能# 思路:# 用户输入用户名.密码# 将用户输入的内容按照固定的格式,比如:egon:123,存入文件# 可以往一个文件中重复注册新的用户名和密码# 附加:# 1.对输入的用 ...
- 从零开始自己搭建复杂网络2(以Tensorflow为例)
从零开始自己搭建复杂网络(以DenseNet为例) DenseNet 是一种具有密集连接的卷积神经网络.在该网络中,任何两层之间都有直接的连接,也就是说,网络每一层的输入都是前面所有层输出的并集, 而 ...
- == 和 equal 区别
在初学 Java 时,可能会经常碰到下面的代码: String str1 = new String("hello"); String str2 = new String(" ...
- poj1195二维树状数组模板
二维树状数组和一维的也差不多,改一下add和query函数即可:即按行修改,行内单点修改即可 /* 二维树状数组,询问一个二维区间内的数之和 */ #include<iostream> # ...
- MVC开发中的常见错误-04-“System.NullReferenceException”类型的异常在 BBFJ.OA.WebApp.dll 中发生,但未在用户代码中进行处理
未将对象引用设置到对象实例,又名空指针异常,伴随程序员开发的一生. 查看详细信息得知: SetUserRoleInfo() 首先想到的是 IBLL.IRoleInfoService RoleInfo ...
- JQuery中jsCharts图表插件(十)
一:1.jsCharts图表插件 注意:从官方下来的例子都没指定页面编码,在这种情况下,浏览器就会使用默认设置中文编码:GB2312,GBK等:导致无法执行. 请在html代码中的<head&g ...