When the publish / subscribe mode encounters NET

Daily development , We usually deploy multiple applications with different roles in the same architecture , These applications need some mechanism to notify each other of what happened . These events may be temporary （ Changes made temporarily at run time ）, It may also be a database event （ Due to changes in the database ）. How to deal with such complex and changeable distributed events , It has always been a rather thorny problem . And this is the release - Where subscription design patterns come into play .

as everyone knows , Release - Subscription patterns are among many design patterns , Probably the most common 、 The most famous one . It defines a one to many relationship , Let multiple subscriber objects listen to a topic object at the same time , When the state of the topic object changes, all subscriber objects that subscribe to it will be notified , So that they can update themselves automatically .

stay “ Release - subscribe ” In the messaging paradigm of , Sender of message （ Publisher ） Do not know the intended recipient （ subscriber ）. Besides , There is no direct interaction between publisher and subscriber applications , It depends on what is called “ The theme ” Public media . therefore , Release - The subscription pattern is a loosely coupled messaging cdxxd Model .

It's based on these characteristics , Release - A subscription model （ Referred to as “ Release / subscribe ”） It has become a way to build an enterprise .NET An indispensable tool for applications .

PART 01

Distributed event driven architecture exploration

To design a distributed event driven architecture , Developers used to prefer one of the following .

1、RDBMS Provide data notification

If data storage is limited to relational databases , The database notification function can indeed . In addition to allowing events to be registered with the database server , This function also updates the result set in the database 、 When changes occur due to addition or deletion , Notify the application side .

But there's a problem ,RDBMS Is essentially non extensible , It can easily become a performance bottleneck for applications . Typically , Developers don't want the database to take on unnecessary extra tasks . Besides , The database notification function itself is also slow , And does not support runtime data sharing .

It's not hard to understand , Using a database as a messaging medium is not the best design choice .

2、 Message queue

Another option is to introduce separate message queues into the architecture . Although these message queues do a good job of helping you transfer messages between applications , But these queues are not data centric , That is, they do not monitor data changes in the database or any other source . Besides , These message queues cannot be extended with the application layer .

3、 Custom solution

The last remaining option is , Create a messaging platform that suits your needs . The idea of a customized solution may seem tempting at first glance , But it may be difficult to predict the time and resources required , Because building and managing a robust and extensible messaging platform is a very difficult task .

The crux of the problem is ： Which solution is easier to merge 、 Scalable 、 Highly available and very reliable ？

PART 02

Using distributed cache as messaging platform

Here we share a message delivery platform using distributed caching NCache. The fact proved that , This is not only a simple and feasible solution , It is also a more modern way to integrate a robust messaging platform .NCache It is the only real local product currently available in the market .NET/.NET Kernel distributed cache . It is a distributed cache technology in memory , Extremely fast , Very scalable . It enables applications to handle extreme transaction loads , Without making the database a bottleneck . Besides , You can also use it NCache Process data in real time / flow .

NCache Usually deployed in N The middle layer of the layer architecture . The following figure shows a more intuitive display of its architecture level .

chart 1：N Layer architecture NCache

NCache Is a cache server cluster , Can be .NET Application and Java Applications provide tens of thousands of requests —— By storing frequently used data in memory , So as to effectively avoid a large number of database access .

below , In depth analysis NCache. First , Let's see NCache The principle of message bus as an event driven architecture .

1、NCache Event driven messages

The image below shows NCache How to act as .NET and Java The message bus function of the application .

chart 2：NCache As a messaging platform

In the architecture above ,NCache Cross platform communication by using fast and compact serialization , This serialization can be converted to .NET or Java Object to binary , Then transfer them to the cache cluster . therefore , This gives NCache How to support .NET Application and Java The inherent logic of application interaction . More information about this , Please search for portable data types by yourself .

NCache Manage publishing with the name of the event / Subscription design pattern , And provide different ways to propagate messages to other listening applications . Let's look at these two message types , To understand how distributed caches propagate them .

First , Consider the data changes that your application needs to listen for . because NCache Is also used .NET Key value storage technology , It provides the ability to update the application when any data changes in the cache . Because all this happens in memory , So there is no performance bottleneck . These data changes can be ：

• Cache level item changes , Whether it's updating or deleting
• The entire cache level data changes
• Continuous query , You can register a similar one SQL Query for , To monitor whether the result set changes in the cache . If so , Will notify the application
• If the cluster changes as a result of any new node additions or deletions or crashes .（ For management ）

NCache It also allows the dependency registration of the database , Include SQL、Oracle and OleDb etc. . This helps keep the database and application cache data up to date . A complete list of supported dependency types , Please check the database dependency content , No more details here . These dependencies are data change notifications registered in different data stores ; however , It can make NCache Deal with it . You can also notify the database to NCache Data notification , So as to further enrich the project construction strategy .

On the other hand , If you only want to propagate simple messages to complex .NET or Java object , Then you should use custom messaging . ad locum , An application can generate data and trigger events , The interested listener will receive the event almost instantaneously . More about this , Readers can view articles related to custom events by themselves .

2、NCache Release / subscribe API

NCache Provides memory publishers / subscriber （ Release / subscribe ） Features and dedicated releases / Subscribe to the message store , To support the .NET Web Real time information sharing in applications , Ultimately help applications communicate better .

Release / Subscription mode provides a channel for interested users to publish and subscribe to messages , Naturally decouple publishers and subscribers . Now? , When NCache When acting as a messaging bus , Release / The subscription model benefits from the underlying NCache Distributed architecture and many convenient functions .

3、 Basic framework

Let's first get to know NCache Release / The basic components of subscription and how they work .NCache Release / The general process of subscribing to messages is as follows ： First , Used by publishers ITopic Interface publishes topic messages . Next , Subscribers can create subscriptions to one or more topics , And receive relevant messages . After successful message delivery ,NCache Will receive a confirmation ; otherwise ,NCache Will continue to retry before the message expires （ If expiration information is set ）. Undelivered messages will reside in the cache , Until the expired message is triggered , Please refer to the diagram below .

chart 3：NCache Release / Subscription message mechanism

4、 Subscription type

NCache For the release of / Subscription messages provide two different types of subscriptions , That is, non persistent subscription and persistent subscription . Besides ,NCache Support exclusive and shared subscription policies . The details are discussed below .

• Non durable subscriptions ： By default , All subscriptions created on the topic are non persistent . It only sends the expected message to the subscriber before the connection is maintained . If the subscriber's connection is lost for any reason , You will not receive an old message when you rejoin the network . This type of subscription is exclusive , This means that a subscription belongs to only one subscriber
• Persistent subscription ： It takes into account the loss of messages when the subscriber disconnects .NCache Keep the subscriber's subscription when the connection is lost . therefore , Subscribers can receive their published messages of interest when reconnecting

Persistent subscription provides two strategies ：

• exclusive ： One subscription at a time belongs to only one active subscriber
• Shared ： A subscription can register multiple subscribers at the same time , And provide load sharing

PART 03

NCahce Release / Subscribe to application cases

Suppose there is an e-commerce store , Different suppliers regularly provide new products to the store . meanwhile , It also provides product sales and discounts . Store managers and customers interested in the products offered need to keep abreast of new products 、 Update on products for sale and discounts .NCache Release / The subscription function enables the distributed notification system in this scenario . So , You can first create NCache Dedicated release / Subscribe to the message store .

Next , Let's talk about using in the above scenario NCache Release / Subscribe to news API The step-by-step process of implementing distributed messages .

1、 Create a theme

As a first step , You need to create a theme , So that different suppliers can release new product updates . have access to NCache Medium ITopic Interface to create a new topic with a unique name . The following code shows how the publisher application uses methods CreateTopic To create a name newProducts The theme of .

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       // Prerequisite ： Cache connected 
       
       
// Specify the subject name 
       
       
string topicName = “newProducts”
       
       
// Create a theme 
       
       
ITopic topic = cache.MessagingService.CreateTopic(topicName);
      
      
      
      

       
       
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If a topic with the provided name already exists , An instance of this topic will be used as ITopic return .

NCache Allows you to set the topic priority when creating a topic . When some events need to be communicated at a higher priority than others , It's very useful . for example , Information about manufactured goods is urgent ; Again , Product price updates due to discounts or sales are for seller / It is also the most important for the buyer . under these circumstances , You can set the topic priority to high when creating a topic , And can receive relevant notifications without delay .

2、 Release the news

After creating a theme , Publisher applications can use Publish Method to publish relevant messages to the topic . So , First, get the instance of the topic by specifying the topic name .NCache There are two delivery modes for publishing messages ：

• All（ Default ）： Deliver the message to all registered subscribers . When broadcasting information is required , It's very useful .
• Any： Deliver the message to any registered subscriber .

Besides , To manage your releases effectively / Subscription cache storage space , You can also set the message expiration time .

In the following code , The publisher will be in the existing theme newProducts Broadcast news about new products on .

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       // Prerequisite ： Cache connected 
       
       
// The theme “newProducts” Created 
       
       
string topicName = "newProducts"
       
       
// Get theme 
       
       
ITopic productTopic = cache.MessagingService.GetTopic(topicName);
       
       
// Create an object to send in a message 
       
       
Product product = FetchProductFromDB(10248);
       
       
// Create a new message corresponding to the order of the objects 
      
      
      
      

       
       
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3、 Subscribe to topic news

After creating a theme , A subscriber application can receive messages published to the topic by obtaining a subscription . Because it supports different types of subscriptions , Therefore, subscribers interested in non persistent subscriptions can use CreateSubscription Method ; For persistent subscriptions , You can use CreateDurableSubscription Method .

The following code shows how the subscriber application is themed newProducts Create subscription .MessageReceived Register a callback to perform any expected actions when a notification is received . for example , Subscribers can receive a sales notice at MessageReceived Update the product price in the callback .

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       // Prerequisite ： Cache connected 
       
       
// The theme “newProducts” Created 
       
       
string topicName = "newProducts"
       
       
// Get theme 
       
       
ITopic productTopic = cache.MessagingService.GetTopic(topicName);
       
       
// Create and register topics newProducts Subscribers 
       
       
// Specify the callback function MessageReceived
       
       
ITopicSubscription orderSubscriber = orderTopic.CreateSubscription(MessageReceived);
      
      
      
      

       
       
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In the example above , Created a non persistent subscription . Besides , When you need to receive old messages from a subscribed topic when reconnecting , Subscribers can create persistent subscriptions .

NCache A pattern - based subscription method is also provided , among NCache Multiple wildcards are supported to subscribe to a single... In the provided mode / Multiple themes .

4、 Registration notice

NCache Enable publishers to understand the status of messages and the availability of topics . The publisher application can register the following notifications ：

• MessageDeliveryFailure： If the message cannot be delivered due to any problems , Then notify the publisher
• OnTopicDeleted： Notify the publisher when a message is deleted

Here is a simple way for publishers to register for both notifications ：

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       // You have an instance of an existing topic productTopic
       
       
// Failed to register messaging 
       
       
productTopic.MessageDeliveryFailure += OnFailureMessageReceived;
       
       
// Register subject deletion notification 
       
       
productTopic.OnTopicDeleted = TopicDeleted;
      
      
      
      

       
       
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By following the above steps , You can publish the basic / The subscription message architecture is integrated into any one ASP.NET perhaps .NET In the core application .

PART 04

summary     

thus , To sum up NCache Release / What benefits does the subscription model offer to overcome the limitations of existing solutions .

• Because of its linear scalability ,NCache Release / Subscriptions can handle more and more subscription requests by adding cache servers and performing load balancing frequently . This scaling feature is transparent to the user , And will not interfere with the communication process . therefore , You can use NCache Release / Subscription mode to easily extend communication performance .
• NCache Release / Subscriptions help keep subscriptions going 、 Notification of message delivery failure and delivery failure , To avoid message loss . Besides ,NCache Our distributed and replication architecture ensures NCache High availability , To accommodate subscriber connections in a dynamic environment . All these features ensure reliable communication .
• because NCache Is a distributed cache in memory , So the message store itself that resides in the cache is very fast . Besides ,NCache Allows you to specify whether data items that reside in the cache expire , To intelligently manage storage space .

NCache extensibility 、 Reliability and storage efficiency , And release / Loosely coupled and asynchronous messaging patterns for subscriptions , bring NCache Release / Subscription function in the future .NET/NET The core application has great prospects in the development of distributed messaging .