Event bus

What is a thing

Things Everything that is seen is a thing, and everything that cannot be seen is a thing

For example: team microservices, member microservices, aggregation microservices, gateway apis, certification authority, and more including classes, objects

All events are the result of changes in things

You’ve been exposed to events for the first time in js or c# advanced features. People don’t default to events, but they don’t understand them very well

What is an event

An event is a change in the state of things, and the result of each change of things is called an event

What is an event bus

A mechanism for managing all events is called an event bus

Including event publishing, event storage, event subscription, event processing collectively

Function:

An event bus is a mechanism that allows different components to communicate with each other without understanding each other. Components can send events to Eventbus without knowing who is answering or how many other people are answering. Components can also listen for events on Eventbus without knowing who sent the event. In this way, components can communicate with each other without having to depend on each other. Again, it’s easy to replace a component. As long as the new component knows about the events being sent and received, the other components will never know.

Why use the event bus

Decouple the components of the microservice system

Use the development of the business

Event Bus framework

CAP

masstransit

Internal concept of CAP

Events: Are status information

Publisher: Cap, the role that publishes the event

Subscriber: Cap subscribes to the role of consuming events

Message transporter: Transmits events

Message storage: Stores events

CAP stores the event message queue type Transport

Azure

rabbitmq

kafaka

In Memory Queue

CAP stores the event persistence type

SQL Server

MySQL

PostgreSQL

MongoDB

InMemoryStorage

CAP Event Monitoring

Dashboard

How to use CAP in microservice system

conditions

1. Microservice system

2, the RabbitMQ

3, essentially

4, CAP

steps

1. Preparation of microservice system

The microservice system is all set up

2. Prepare RabbitMQ

2.1 Environment Preparation

Download Erlang from www.erlang.org/downloads

The RabbitMQ download address: www.rabbitmq.com/download.ht…

2.2 the RabbitMQ start

1. Add the visual plug-in in the installation directory

rabbitmq-plugins enable rabbitmq_management
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2. Start in the installation directory

	rabbitmq-server 
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3. Check the rabbitMQ status

    rabbitmqctl status
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4. Enter http://127.0.0.1:15672 in the browser

Access the RabbitMQ background system

3. Prepare SqlServer

SqlServer is started and installed

4. CAP preparation

4.1 CAP environment

Cap.dotnetcore.xyz /user-guide/…

4.2 CPA configuration

1, in RuanMou. MicroService. Add rely on the Core project

CAP Nuget dotnetcore. CAP CAP Transport Nuget dotnetcore.cap. RabbitMQ CAP Persist dotnetcore.cap. SqlServerCopy the code

2, in RuanMou. MicroService. AggregateService service startup. Cs to add

AddCap(x => {// 8.1 Using memory to Store Messages (Handling message sending failures). RabbitMQ(rb => {rb.HostName = "localhost"; // 8.2 Using RabbitMQ for event center processing. rb.UserName = "guest"; rb.Password = "guest"; rb.Port = 5672; rb.VirtualHost = "/"; }); });Copy the code

2.1 Inject ICapPublisher into Aggregatecontroller.cs

    private readonly ICapPublisher capPublisher;
public TeamsController(ICapPublisher capPublisher)
    {
        this.capPublisher = capPublisher;
    }	
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3, in RuanMou. MicroService. VideoService service startup. Cs to add

AddCap(x => {// 8.1 UseRabbitMQ for event center processing. userabbitmq (rb => {rb.HostName = "localhost"; rb.UserName = "guest"; rb.Password = "guest"; rb.Port = 5672; rb.VirtualHost = "/"; }); });Copy the code

3.1 Adding features to methods in VideoController.cs [CapSubscribe]

/ / / < summary > / / / Video add add (asynchronous) / / / < summary > / / / < param name = "Video" > < param > / / / < returns > < / returns > [NonAction] [CapSubscribe("tontcap")] public ActionResult<Video> PostVideo(Video Video) { videoService.Create(Video); return CreatedAtAction("GetVideo", new { id = Video.Id }, Video); }Copy the code

4. Effect display

RabbitMQ is down

steps

1. Disable RabbitMQ

The event message could not be sent and was stored in memory cache

2. When RabbitMQ is started, messages are sent normally

Internal use of timer polling mechanism

AggregateService breakdown

The AggregateService runs services successfully, but breaks down before sending messages

Solution using local message tables (idea: persistent operations)

conditions

1. Local message table

steps

1, in RuanMou. MicroService. AggregateService services

1.1 Create a Context file, and then create AggregateContext in the Context folder

// </summary> // Aggregate service context /// </summary> public class AggregateContext: DbContext { public AggregateContext(DbContextOptions<AggregateContext> options) : base(options) { } }Copy the code

1.2 Add in AppSettings. json

{ "ConnectionStrings": { "DefaultConnection": "Data Source=.; Initial Catalog=aggregateservice; Persist Security Info=True; User ID=sa; Password=tony" } }Copy the code

1.3 Adding message persistence in startup.cs

AddDbContext<AggregateContext>(options => { options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")); }); AddCap(x => {// 8.1 Using EntityFramework for storage operations. / / 8.2 using essentially the transaction x.U seSqlServer (Configuration. The GetConnectionString (" DefaultConnection ")); RabbitMQ(rb => {rb.HostName = "localhost"; // 8.2 Using RabbitMQ for event center processing. rb.UserName = "guest"; rb.Password = "guest"; rb.Port = 5672; rb.VirtualHost = "/"; }); });Copy the code

1.4 Test demonstration effect

There are two more tables in the database

​

When the business is successfully executed and the message is sent, the converged microservice goes down and the message is persisted to the database

When the converged micro service is restarted, the message is successfully sent and consumed

1.5 the principle

1. Timer message retry

2. Idempotence A function has the same result every time and only one state

VideoService breakdown

VideoService failed to accept the message

Failed to receive messages when VideoService directly went down.

Then restart VideoService message consumption successfully

VideoService failed to receive message successfully

conditions

1. Local message table

steps

1, in RuanMou. MicroService. The Core project

1.1 installation is essentially

Nuget DotNetCore.CAP.SqlServer
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2, in RuanMou. MicroService. VideoService project

2.1 Adding message persistence in startup.cs

AddCap(x => {// 8.1 Using EntityFramework for storage operations. / / 8.2 using essentially the transaction x.U seSqlServer (Configuration. The GetConnectionString (" DefaultConnection ")); RabbitMQ(rb => {rb.HostName = "localhost"; // 8.2 Using RabbitMQ for event center processing. rb.UserName = "guest"; rb.Password = "guest"; rb.Port = 5672; rb.VirtualHost = "/"; }); });Copy the code

2.2 Effect Display

There are two more tables in the database

2.3 the principle

1. Timer message retry

2. Idempotence A function has the same result every time and only one state

Message retry or consumption failure

Using human intervention

conditions

1. Dashboard – Background management page

steps

1, in RuanMou. MicroService. The Core project

1.1 installation Dashboard

Nuget DotNetCore.CAP.Dashboard
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2, in RuanMou. MicroService. VideoService project

2.1 Adding a Dashboard to startup.cs

AddCap(x => {// 8.1 Using EntityFramework for storage operations. / / 8.2 using essentially the transaction x.U seSqlServer (Configuration. The GetConnectionString (" DefaultConnection ")); // 8.3 Using RabbitMQ for event center processing. User AbbitMQ (rb => {rb.HostName = "localhost"; rb.UserName = "guest"; rb.Password = "guest"; rb.Port = 5672; rb.VirtualHost = "/"; }); // 8.4 Adding the background Monitoring page of CAP x. user Dashboard(); });Copy the code

2.2 Open the CAP background monitoring page

​ http://localhost:5007/cap

The message that fails to be sent is repeated

Re-consume messages that fail to consume