Use and expansion of fault tolerance and fusing

One 、 Introduction of fault tolerance mechanism

• Concept
  When the client invokes the microservice , There's a problem , Be able to fail over , Fault tolerance mechanism .
  Pictured ：
  

• Purpose
  Ensure high availability of microservices .

Two 、 Why use fault tolerance

• Failover mechanism
  Pictured ：
  

3、 ... and 、 How to apply fault tolerance mechanism in microservices

• Implementation conditions
  • while
• Implementation steps

      int count = 0;
      // Fail over 
      for(int i=0;i<=3;i++)
      {
           // Judge whether the threshold is reached 
           if (count == 3)
           {
             // Exit loop , Return exception information 
             throw  Exception(" The microservice retry operation exceeded the threshold ");
           } 
           // Business code 
           try
           {
              // HttpClient  Request microservice code 
              ...................
           }
           catch(Exception  ex)
           {
               // Capture exception information  
               count ++;   
           }
      } 
  

Four 、 Defects of fault-tolerant mechanism

• defects
  • Low performance , Resource consumption
  • Solution
    • Set a fixed number of times
    • Use circuit breakers

5、 ... and 、 How to use in micro service system Polly

• Fuse
  • Concept
    The fuse is a request .
    When the request arrives at the server , The request was retried 3 Time 【 Number of tests 】, No request succeeded , Directly fuse the request , Please come in next time , Don't try again , Return exception information directly .
• Conditions
  • Polly
• Code implementation
  • Conditions
    • install Polly
  • step
    • install

       Microsoft.Extensions.Http.Polly
      

    • stay Startup.cs Register in the file
      • Method name ConfigureServices

           // Abnormal degradation information  
             var fallBack = new HttpResponseMessage(){ 
                 Content = new StringContent(" The system is busy ！"),
                 StatusCode = 504
             };
           //5： Circuit breaker threshold 
           //10： Melting time 
           //ExecutionRejectedException: Capture all abnormal information of fuse 
           //10： Total number of threads used 
            services.AddHttpClient("micro[ Request reuse ： Custom name ]")
                .AddPolicyHandler(Policy<HttpResponseMeaage>.Handle<ExecutionRejectedException>().Fallback(fallBack))  // Abnormal information degradation 
                .AddPolicyHandler(Policy<HttpResponseMeaage>.Handle<Exception>().CircuitBreakerAsync(5,TimeSpan.FromSeconds(10))) // Circuit breaker 
                .AddPolicyHandler(Policy.TimeoutAsync<HttpResponseMeaage>(60))// Set timeout 
                .AddPolicyHandler(Policy<HttpResponseMeaage>.Handle<Exception>().RetryAsync(1))// Retry count 
                .AddPolicyHandler(Policy.BulkheadAsync<HttpResponseMeaage>(10,100));// resources （ Threads ） Isolation   //10： Total number of threads used   100: Total request cache 
        

      • Business code

            private HttpClientFactory _httpClientFactory;
            // Inject... Into the constructor 
             Constructors (HttpClientFactory httpClientFactory)
            {
              _httpClientFactory = httpClientFactory;
            }      
            
          int count = 0;
          // Fail over 
          for(int i=0;i<=3;i++)
          {
               // Judge whether the threshold is reached 
               if (count == 3)
               {
                 // Exit loop , Return exception information 
                 throw  Exception(" The microservice retry operation exceeded the threshold ");
               } 
               // Business code  
               try
               {
                 // Microservice request 
                 HttpClient client = _httpClientFactory.CreateClient("micro");
                 .........
               }
               catch(HttpRequestException  ex)
               {  
                   // Capture exception information  
                   count ++;   
               }
          } 
           
        

6、 ... and 、 Microservice fault tolerance mechanism Polly Expand

• If two microservices are called at the same time in the aggregated microservice , When the first service hangs up , In order not to affect the subsequent service calls , We need to do service isolation , The code is as follows ：
  • stay Startup.cs Register in the file
    • Method name ConfigureServices

          services.AddHttpClient(" Define different names according to different services ")
                    .AddPolicyHandler(Policy<HttpResponseMeaage>.Handle<ExecutionRejectedException>().Fallback(fallBack))  // Abnormal information degradation 
                    .AddPolicyHandler(Policy<HttpResponseMeaage>.Handle<Exception>().CircuitBreakerAsync(5,TimeSpan.FromSeconds(10))) // Circuit breaker 
                    .AddPolicyHandler(Policy.TimeoutAsync<HttpResponseMeaage>(60))// Set timeout 
                    .AddPolicyHandler(Policy<HttpResponseMeaage>.Handle<Exception>().RetryAsync(1))// Retry count 
                    .AddPolicyHandler(Policy.Bulkhead<HttpResponseMeaage>(10,100));// Resource isolation 
      

      Be careful ： When http On request , The name of each service requested must be consistent with the registered name .
  • Caller code

      HttpClient client = _httpClientFactory.CreateClient(" Define different names according to different services ");