SpringCloud（二）Hystrix服务容错-搜云库技术团队

1.Hystrix基本概念

Hystrix is a latency and fault tolerance library designed to isolate points of access to remote systems, services and 3rd party libraries, stop cascading failure and enable resilience in complex distributed systems where failure is inevitable.

What does it do?

1、 Latency and Fault Tolerance Stop cascading failures. Fallbacks and graceful degradation. Fail fast and rapid recovery.

Thread and semaphore isolation with circuit breakers.

1、 Realtime Operations Realtime monitoring and configuration changes. Watch service and property changes take effect immediately as they spread across a fleet.

Be alerted, make decisions, affect change and see results in seconds.

1、 Concurrency Parallel execution. Concurrency aware request caching. Automated batching through request collapsing.

⚠️注意：Hystrix官方已停止对其的维护

2.基于Hystrix构建服务

我们这里构建两个服务，书店服务BookStore，提供图书借阅服务；读者服务Reading，远程调用书店的借阅服务，使用Hystrix对Reading的远程调用进行包装。（是的，Hystrix是在上游的调用方进行配置）

2.1.构建BookStore服务

BookstoreApplication.java

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.RequestMapping;

@RestController
@SpringBootApplication
public class BookstoreApplication {

  @RequestMapping(value = "/recommended")
  public String readingList(){
    return "BookStore 调用成功，祝阅读愉快";
  }

  public static void main(String[] args) {
    SpringApplication.run(BookstoreApplication.class, args);
  }
}

BookStore/resources/application.properties

server.port=8090

2.2.构建读者服务

ReadingApplication.java

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.client.RestTemplateBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.web.client.RestTemplate;

@EnableCircuitBreaker   #启用hystrix进行熔断
@RestController
@SpringBootApplication
public class ReadingApplication {

  @Autowired
  private BookService bookService;

  @Bean
  public RestTemplate rest(RestTemplateBuilder builder) {
    return builder.build();
  }

  @RequestMapping("/to-read")
  public String toRead() {
    return bookService.readingList();
  }

  public static void main(String[] args) {
    SpringApplication.run(ReadingApplication.class, args);
  }
}

最关键的一步，使用Hystrix包装远程调用方法 BookService.java

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;
import java.net.URI;

@Service
public class BookService {

  private final RestTemplate restTemplate;

  public BookService(RestTemplate rest) {
    this.restTemplate = rest;
  }

  @HystrixCommand(fallbackMethod = "reliable")  #远程服务失败，则回调fallbackMethod
  public String readingList() {
    URI uri = URI.create("http://localhost:8090/recommended");

    return this.restTemplate.getForObject(uri, String.class);
  }

  public String reliable() {
    return "BookStore 调用失败";
  }

}

Reading/resources/application.properties

server.port=8080

2.3.测试

分别启动BookstoreApplication和ReadingApplication

访问 localhost:8080/to-read

停止BookstoreApplication，再次访问localhost:8080/to-read，可以看到，hystrix已启用了熔断

3.Hystrix Dashboard

同时，Hystrix还有一套自我监控体系——Hystrix Dashboard。Hystrix Dashboard可以对Hystrix进行监控，并提供可视化监测，方便开发、运维人员随时查看当前服务将康状态。接下来我们来构建Hystrix DashBoard。

3.1.修改Reading服务

配置Reading服务暴露actuator，同时配置hystrix.stream，使得其可以被Hystrix Dashboard监测到。（同时在pom.xml添加相应依赖）

Reading/resources/application.properties

server.port=8080
management.server.port=8888
management.endpoint.health.show-details=always
management.endpoints.web.exposure.exclude='*'
management.endpoints.web.exposure.include='hystrix.stream'

3.2.构建Hystrix Dashboard服务

新建一个Spring工程，HystrixDashboard

HystrixDashboardApplication.java

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.hystrix.dashboard.EnableHystrixDashboard;

@SpringBootApplication
@EnableHystrixDashboard
public class HystrixDashboardApplication {
  public static void main(String[] args) {
    SpringApplication.run(HystrixDashboardApplication.class, args);
  }
}

建立HystrixIndexController，提供一个对外接口 HystrixIndexController.java

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;

@Controller
public class HystrixIndexController {
  @GetMapping("")
  public String index() {
    return "forward:/hystrix";
  }
}

HystrixDashboard/resources/application.properties