SpringCloud Alibaba actual combat (9: Hystrix fault-tolerant protection)

Posted by coolbeansdude51 on Mon, 24 Jan 2022 00:02:35 +0100

Source address: https://gitee.com/fighter3/eshop-project.git

Continuously updating

In the previous section, we have used OpenFeign to complete the call between services. Think about it. If there are more than a dozen services upstream and downstream of a service link, and each service has several nodes, one of which fails, the upstream request hits the failed node, and the join request is blocked all the time. A large number of accumulated requests may collapse the service, may lead to cascading failure, or even the failure of the whole link. This is the so-called service avalanche, Serious may directly cause the system to hang up. In order to avoid this terrible situation, the necessary fault-tolerant protection mechanism is necessary.

1. Introduction to Hystrix

Hystrix is an important component of Netflix, providing circuit breaker, resource isolation and self-healing functions.

The following is Hystrix as a circuit breaker to prevent cascading failure.

But hystrix1 After version 5.18, we entered the maintenance mode, and we adopted this version. In the system of spring cloud and Alibaba, sentinel, another component, can be used as a substitute, which we will use later.

Although the update of Hystrix has stopped, it is now a relatively mature product after years of iteration, so it is still widely used.

The use of Hystrix in the spring cloud system is also very simple. Let's start now!

2. Introducing Hystrix

We still use the example in the previous section.

Spring cloud starter is adopted to introduce:

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

In application YML enable hystrix:

feign:
  hystrix:
    enabled: true

Add the @ EnableHystrix annotation to the service startup class to enable the system to support the functions of hystrix.

@SpringBootApplication
@MapperScan("cn.fighter3.mapper")
@EnableDiscoveryClient
@EnableFeignClients(basePackages = "cn.fighter3.client")
@EnableHystrix
public class EshopGoodsApplication {

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

Write a StockClientFallback class to implement the StockClientFeign interface. What is this class used for? It is used for Feign client remote call failure callback.

/**
 * @Author Three evil
 * @Date 2021/5/29
 * @Description Inventory service callback exception callback class
 */
@Component
@Slf4j
public class StockClientFallback implements StockClientFeign {

    public Integer addStock(StockAddDTO stockAddDTO) {
        log.error("Inventory service-Add inventory not available!");
        return 0;
    }

    public Integer getAccountById(Integer goodsId) {
        log.error("Inventory service-Get inventory not available!");
        return 0;
    }
}

Add the failed callback configuration in StockClientFeign, which was @ feignclient (value = "stock service")

@FeignClient(value = "stock-service", fallback = StockClientFallback.class)

There is another way to define the service degradation method by using @ HystrixCommand(fallbackMethod = "getDefaultUser") on the method.

3. Test Hystrix

Start the Nacos server and commodity service successively. Note that we did not start the inventory service

Open http://localhost:8020/doc.html , call the add product interface. Think about it. What would happen under normal circumstances? Since the inventory service does not work, the commodity service must return an exception. However, when hystrix is added, it is found that the interface returns a successful result.