springcloud7---hystrix

目前使用eureka server完成了服务注册和服务发现，ribbon完成了客户端负载均衡。如果服务提供者的响应很慢那么服务消费者会强制等待，一直等到http请求超时，如果服务消费者还是其他的服务提供者，那么就会产生级联的雪崩。

超时机制：等待几秒还是没响应，就直接返回了。

断路器模式：A如果有大量的超时，B一直去请求A是没有意义的，不再去请求A直接返回异常。保证B不会拖死。

断路器全开（B不去请求A），断路器半开（过了10分钟，B猜测A是不是好了，留一小部分流量去请求A大部分还是直接抛异常，发现A响应时间/失败率达标了就把断路器关闭）

容错：雪崩效应。CD的微服务调了B的接口，B又调了A的接口。A宕机了，B里面就会堆积线程，接着B宕机了，CD里面堆积线程，接着CD宕机了。

5秒钟失败20次就打开。

实践：

1.监控：判断A是不是挂掉了（有一个阈值，请求多少次有多少次失败了）。

2.断路器状态：打开，关闭，半开。

3.分流：留小部分流量尝试请求A服务。

4.自我修复：断路器状态切换

超时机制：高并发下，A挂了，设置超时机制，内网传输很快。

断路器：B调用A出现了异常，并不会立即扔到断路器里面去，比如达到60%都是异常状态，就会丢到断路器里面去，B就不请求A了。

断路器打开了，过一段时间看A微服务是否已经修复了，就小部分流量去请求（判断是否达到阈值），如果还是失败就继续打开（继续直接返回），如果好了就关闭。

ribbon整合hystrix：

package com.itmuch.cloud;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
@EnableEurekaClient
@EnableCircuitBreaker  //启用断路器
public class ConsumerMovieRibbonApplication {

  @Bean
  @LoadBalanced  //ribbon的客户端负载均衡
  public RestTemplate restTemplate() {
    return new RestTemplate();
  }

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

package com.itmuch.cloud.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

import com.itmuch.cloud.entity.User;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;

@RestController
public class MovieController {
  @Autowired
  private RestTemplate restTemplate;

  //http://localhost:8010/movie/1
  //查看hystrix的状态http://localhost:8010/hystrix.stream
  //第一次会进fallbackMethod方法，后面走microservice-provider-user。因为Hystrix默认超时时间是1秒。
  //microservice-provider-user挂了就进fallbackMethod
  @GetMapping("/movie/{id}")
  @HystrixCommand(fallbackMethod = "findByIdFallback")  //参数和返回值类型一样，当用户微服务挂了就走fallbackMethod。进入了fallbackMethod不代表断路器打开。
  public User findById(@PathVariable Long id) {
    return this.restTemplate.getForObject("http://microservice-provider-user/simple/" + id, User.class);
  }

  public User findByIdFallback(Long id) {
    User user = new User();
    user.setId(0L);
    return user;
  }
}

package com.itmuch.cloud.entity;

import java.math.BigDecimal;

public class User {
  private Long id;

  private String username;

  private String name;

  private Short age;

  private BigDecimal balance;

  public Long getId() {
    return this.id;
  }

  public void setId(Long id) {
    this.id = id;
  }

  public String getUsername() {
    return this.username;
  }

  public void setUsername(String username) {
    this.username = username;
  }

  public String getName() {
    return this.name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public Short getAge() {
    return this.age;
  }

  public void setAge(Short age) {
    this.age = age;
  }

  public BigDecimal getBalance() {
    return this.balance;
  }

  public void setBalance(BigDecimal balance) {
    this.balance = balance;
  }

}

spring:
  application:
    name: microservice-consumer-movie-ribbon-with-hystrix
server:
  port: 8010
eureka:
  client:
    healthcheck:
      enabled: true
    serviceUrl:
      defaultZone: http://user:password123@localhost:8761/eureka
  instance:
    prefer-ip-address: true
hystrix.command.default.execution.isolation.thread.timeoutInMilliseconds: 5000

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <artifactId>microservice-consumer-movie-ribbon-with-hystrix</artifactId>
    <packaging>jar</packaging>

    <parent>
        <groupId>com.itmuch.cloud</groupId>
        <artifactId>microservice-spring-cloud</artifactId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-eureka</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        
        <!-- 添加依赖 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-hystrix</artifactId>
        </dependency>
    </dependencies>
</project>

package com.itmuch.cloud.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

import com.itmuch.cloud.entity.User;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixProperty;

@RestController
public class MovieController {
  @Autowired
  private RestTemplate restTemplate;

  @GetMapping("/movie/{id}")
  @HystrixCommand(fallbackMethod = "findByIdFallback", commandProperties = @HystrixProperty(name = "execution.isolation.strategy", value = "SEMAPHORE"))
  //配置上面之后findById方法和fallbackMethod的方法在一个线程里面
  public User findById(@PathVariable Long id) {
    return this.restTemplate.getForObject("http://microservice-provider-user/simple/" + id, User.class);
  }

  public User findByIdFallback(Long id) {
    User user = new User();
    user.setId(0L);
    return user;
  }
}

        <!-- 使用http://localhost:8010/health要有这个依赖 -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>