Hystrix断路器

Hystrix断路器

• https://github.com/Netflix/Hystrix/wiki
  
  

微服务宕机时,ribbon无法转发请求

• 关闭其中一个服务,并通过ribbon访问,则无法访问到

Hystrix入门

1.创建项目导入坐标

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.3.2.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>cn.tedu</groupId>
    <artifactId>sp07-hystrix</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>sp07-hystrix</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>Hoxton.SR6</spring-cloud.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-netflix-eureka-client</artifactId>
            <exclusions>
                <exclusion>
                    <artifactId>jackson-dataformat-xml</artifactId>
                    <groupId>com.fasterxml.jackson.dataformat</groupId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>cn.tedu</groupId>
            <artifactId>sp01-commons</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.retry</groupId>
            <artifactId>spring-retry</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

2.添加hystrix起步依赖

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

3.修改 application.yml

server:
  port: 3001
spring:
  application:
    name: hystrix-server
eureka:
  client:
    service-url:
      defaultZone: http://eureka1:2001/eureka,http://eureka2:2002/eureka
ribbon:
  MaxAutoRetriesNextServer: 2
  MaxAutoRetried: 1

4.主程序添加@EnableCircuitBreaker启用hystrix断路器

启动断路器，断路器提供两个核心功能：

• 降级，超时、出错、不可到达时，对服务降级，返回错误信息或者是缓存数据

• 熔断，当服务压力过大，错误比例过多时，熔断所有请求，所有请求直接降级

• 可以使用 @SpringCloudApplication 注解代替三个注解@EnableCircuitBreaker@EnableDiscoveryClient@SpringBootApplication

5.RibbonController中添加降级方法

• 为每个方法添加降级方法，例如 getItems() 添加降级方法 getItemsFB()
• 添加 @HystrixCommand 注解，指定降级方法名

@RestController
public class RibbonController {
	@Autowired
	private RestTemplate rt;
	
	@GetMapping("/item-service/{orderId}")
	@HystrixCommand(fallbackMethod = "getItemsFB") //指定降级方法的方法名
	public JsonResult<List<Item>> getItems(@PathVariable String orderId) {
		return rt.getForObject("http://item-service/{1}", JsonResult.class, orderId);
	}

	@PostMapping("/item-service/decreaseNumber")
	@HystrixCommand(fallbackMethod = "decreaseNumberFB")
	public JsonResult decreaseNumber(@RequestBody List<Item> items) {
		return rt.postForObject("http://item-service/decreaseNumber", items, JsonResult.class);
	}
	/

    //降级方法的参数和返回值，需要和原始方法一致，方法名任意
	public JsonResult<List<Item>> getItemsFB(String orderId) {
		return JsonResult.err("获取订单商品列表失败");
	}
	public JsonResult decreaseNumberFB(List<Item> items) {
		return JsonResult.err("更新商品库存失败");
	}
}

hystrix超时设置

超时设置

hystrix.command.default.execution.isolation.thread.timeoutInMilliseconds
hystrix等待超时后, 会执行降级代码, 快速向客户端返回降级结果, 默认超时时间是1000毫秒

为了测试 hystrix 降级，我们把 hystrix 等待超时设置得非常小（500毫秒）

此设置一般应大于 ribbon 的重试超时时长，例如 10 秒

server:
  port: 3001
spring:
  application:
    name: hystrix-server
eureka:
  client:
    service-url:
      defaultZone: http://eureka1:2001/eureka,http://eureka2:2002/eureka
ribbon:
  MaxAutoRetriesNextServer: 2
  MaxAutoRetried: 1
hystrix:
  command:
    default:
      execution:
        isolation:
          thread:
            timeoutInMilliseconds: 500

启动项目进行测试

• 可以看到，如果 item-service 请求超时，hystrix 会立即执行降级方法

• 访问 user-service，由于该服务未启动，hystrix也会立即执行降级方法