Spring Cloud Getting Started tutorial-hystrix circuit breaker for fault tolerance and demotion

Brief introduction

Spring Cloud provides a hystrix fault-tolerant library to temporarily invoke an alternate method when the service is unavailable, and a downgrade strategy is implemented for the method that configures the circuit breaker. This article creates a product microservices, registers to the Eureka Service registry, and then we use the Web Client Access /products API to obtain a list of products that, when a product service fails, calls the local fallback method to downgrade but to provide the service normally.

Basic Environment

• JDK 1.8
• Maven 3.3.9
• IntelliJ 2018.1
• Git

Project Source

Gitee Code Cloud

Add a product service

Create a new MAVEN project in IntelliJ, using the following configuration

• GroupId:cn.zxuqian
• Artifactid:productservice

Then add the following code in the Pom.xml:

<?xmlVersion= "1.0" encoding= "UTF-8"?><projectxmlns="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>    <groupId>Cn.zxuqian</groupId>    <artifactId>Productservice</artifactId>    <version>1.0-snapshot</version>    <parent>        <groupId>Org.springframework.boot</groupId>        <artifactId>Spring-boot-starter-parent</artifactId>        <version>2.0.1.RELEASE</version>        <relativePath/>    </parent>    <properties>        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>        <java.version>1.8</java.version>    </properties>    <dependencies>        <dependency>            <groupId>Org.springframework.cloud</groupId>            <artifactId>Spring-cloud-starter-netflix-eureka-client</artifactId>        </dependency>        <dependency>            <groupId>Org.springframework.cloud</groupId>            <artifactId>Spring-cloud-starter-config</artifactId>        </dependency>        <dependency>            <groupId>Org.springframework.boot</groupId>            <artifactId>Spring-boot-starter-web</artifactId>        </dependency>        <dependency>            <groupId>Org.springframework.boot</groupId>            <artifactId>Spring-boot-starter-test</artifactId>            <scope>Test</scope>        </dependency>    </dependencies>    <dependencyManagement>        <dependencies>            <dependency>                <groupId>Org.springframework.cloud</groupId>                <artifactId>Spring-cloud-dependencies</artifactId>                <version>Finchley.m9</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>    <repositories>        <repository>            <id>Spring-milestones</id>            <name>Spring Milestones</name>            <url>Https://repo.spring.io/libs-milestone</url>            <snapshots>                <enabled>False</enabled>            </snapshots>        </repository>    </repositories></project>

We continue to use it spring-cloud-starter-netflix-eureka-client to automate the registration of product services to the Eureka service. A spring-cloud-starter-config configuration file that reads the Configuration service center is also used. This project is just a simple spring Web project.

src/main/resourcesunder Create a bootstrap.yml file, add the following:

spring:  application:    name: product-service  cloud:    config:      uri: http://localhost:8888

Create a file in the configuration center git repository to product-service.yml add the following configuration and commit:

server:  port: 8081

This configuration specifies that the port for the product service is 8081. Then create Application the class, adding the following code:

package cn.zxuqian;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.cloud.client.discovery.EnableDiscoveryClient;@EnableDiscoveryClient@SpringBootApplicationpublicclass Application {    publicstaticvoidmain(String[] args) {        SpringApplication.run(Application.class, args);    }}

@EnableDiscoveryClientThe annotations will instruct spring Cloud to automatically register the service with Eureka. Finally, create cn.zxuqian.controllers.ProductController the controller, provide /products the API, return the sample data:

package cn.zxuqian.controllers;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController;@RestControllerpublicclass ProductController {    @RequestMapping("/products")    publicproductList() {        return"外套，夹克，毛衣，T恤";    }}

Configuring the Web Client

Open the project that we created earlier web , pom.xml add dependencies in the new Hystrix :

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

Then update Application the code for the class:

Package Cn.zxuqian;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import Org.springframework.boot.web.client.RestTemplateBuilder;import Org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;import org.springframework.cloud.client.discovery.EnableDiscoveryClient;import Org.springframework.context.annotation.Bean;import org.springframework.web.client.RestTemplate;@EnableCircuitBreaker@EnableDiscoveryClient@SpringBootApplication Public classApplication { Public Static void Main(string[] args) {springapplication.Run(Application.class, args); }@Bean     PublicResttemplateRest(Resttemplatebuilder builder) {returnBuilder.Build(); }}

This is used here @EnableCircuitBreaker to turn on the circuit breaker function, and then add a rest method and use @Bean annotations. This is part of the spring Dependency injection feature, which uses @Bean markup to tell you how to initialize such an object, such as the one used to create an object in this case, which is later used in a RestTemplateBuilder service that uses a RestTemplate circuit breaker.

Create cn.zxuqian.service.ProductService the class and add the following code:

Package cn.zxuqian.services;import Com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.cloud.client.ServiceInstance;import org.springframework.cloud.client.discovery.DiscoveryClient;import Org.springframework.stereotype.Service;import org.springframework.web.client.RestTemplate;import java.util.List;@Service Public classProductservice {Private FinalResttemplate resttemplate;@Autowired    PrivateDiscoveryclient discoveryclient; Public Productservice(Resttemplate resttemplate) { This.resttemplate= Resttemplate; }@HystrixCommand(Fallbackmethod ="Backupproductlist") PublicStringProductList() {List<serviceinstance> instances = This.discoveryclient.getinstances("Product-service");if(Instances! =NULL&& instances.size() >0) {return  This.resttemplate.Getforobject(Instances.Get(0).GetURI() +"/products", String.class); }return ""; } PublicStringbackupproductlist() {return "jacket, Sweater"; }}

The reason to create a service class is because Hystrix can only be marked as@ServiceOr@Componentclass, so that the API provided by spring context can be used normally. This will be explained later when we delve into spring.
Use@HystrixCommandAfter annotations, Hystrix will monitor the annotated methodproductList(The bottom layer uses proxy wrapper this method to implement monitoring), once the error of this method accumulates to a certain threshold, it will start the circuit breaker, all subsequent callsproductListMethod fails, and the request is temporarily calledfallbackMethodThe specified methodbackupProductList(), and then the circuit breaker shuts down when the service returns to normal.
We also used theDiscoveryClientTo find the URI address of the product service, use the product service'sspring.application.nameThe value of the configuration item, which isproduct-serviceAsserviceIDTodiscoveryClient.getInstances()method, and then returns a list, because currently only one of our product services is started, so we just need to take the URI address of the first instance.
Then we useRestTemplateTo access the API for the product service, note that the spring constructor injection is used@BeanThe annotated method is used to initialize therestTemplatevariables, which do not require us to initialize manually.RestTemplateclass provides agetForObject()method to access other rest APIs and wrap the result in the form of an object, the first parameter is the URI address of the API to be accessed, the second parameter is the type of the result obtained, and here we return a string, so pass it to himString.class。
backupProductList()method returns the product list information after the downgrade.

Finally, create a controller cn.zxuqian.controllers.ProductController and add the following code:

package cn.zxuqian.controllers;  import cn.zxuqian.services.ProductService;  import org.springframework.beans.factory.annotation.Autowired;  import org.springframework.web.bind.annotation.RequestMapping;  import Org.springframework.web.bind.annotation.RestController;   @RestController  public  class  Productcontroller { @Autowired  private  productservice Productservic    E  @RequestMapping     ( "/products" ) public  String productlist  () {return  productservice. (); }}

This ProductService is used to /products provide data for the path.

Test

First, we use spring-boot:run plug-ins to start the Configuration Center service, Config-server, then start Eureka-server, then start Product-service, and finally start the Web client, wait a moment for Eureka service to register successfully after access http://localhost:8080/products, the normal situation will get the 外套，夹克，毛衣，T恤 result, then we close the Product-service, and then access the same path, will be degraded after the result:夹克，毛衣

Welcome to visit my blog http://zxuqian.cn/spring-cloud-tutorial-hystrix/

Spring Cloud Getting Started tutorial-hystrix circuit breaker for fault tolerance and demotion