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Brief introduction

In micro-services, service registration and discovery play a key role in managing each micro-service subsystem. As the system expands more and more horizontally, the number of micro-services split into systems will increase accordingly, so it will be very difficult to manage and obtain the URL of these micro-services. if we add a new micro-service, we have to manually add its URL address or other communication protocol address to other places where the micro-service is used, which will often make mistakes and have a huge workload. Once the address of a microservice changes, it is necessary to manually modify the configuration files of all microservices that reference it. So spring-cloud eureka server is to solve this problem, after a simple configuration, you can automatically register and discover micro-services.

Basic environment JDK 1.8Maven 3.3.9IntelliJ 2018.1Git project source code

Gitee Code Cloud

Set up Eureka Server

In the last blog, we introduced how to build a configuration center for spring-cloud, and a test web client to access it. This time we built an eureka server based on the previous one, read the configuration of the configuration center, and then registered web client as a Discovery Client with the eureka service. First, create a new Maven project under IntelliJ:

GroupId: cn.zxuqianartifactId: registry

Then add the following code to pom.xml:

4.0.0 cn.zxuqian registry 1.0-SNAPSHOT jar org.springframework.boot spring-boot-starter-parent 2.0.1.RELEASE UTF-8 1.8 org.springframework.cloud spring-cloud-starter-netflix-eureka-server org.springframework. Cloud spring-cloud-starter-config org.springframework.boot spring-boot-starter-test test org.springframework.cloud spring-cloud-dependencies Finchley.M9 pom import Org.springframework.boot spring-boot-maven-plugin spring-milestones Spring Milestones https://repo.spring.io/libs-milestone false

Spring-cloud-starter-netflix-eureka-server, the eureka-server core dependency, is used here, as well as the client component spring-cloud-starter-config, which accesses the configuration center service.

Then create the bootstrap.yml file under src/main/resources and add the following configuration:

Spring: application: name: eureka-server cloud: config: uri: http://localhost:8888

This file is configured with the application name used to read the configuration file, spring.application.name, which corresponds to the file name of the service center. In addition, the automatic registration and discovery of Eureka is also based on this parameter. The uri for configuring the service center is then configured.

Create a new Java class, cn.zxuqian.Application, using the following code:

Package cn.zxuqian;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;@EnableEurekaServer@SpringBootApplicationpublic class Application {public static void main (String [] args) {SpringApplication.run (Application.class, args);}}

Here, just use the @ EnableEurekaServer annotation to configure the application as EurekaServer. Then create the eureka-server.yml file in the git repository in the configuration center and add the following configuration:

Server: port: 8761eureka: client: register-with-eureka: false fetch-registry: false

This file configures the port of eureka-server and turns off eureka self-registration and discovery, because if it is not closed, eureka will try to register itself during startup, but will report an error when it finds that the service is not started. At this point, the eureka server is configured.

Update Web Client

Now we need to update web client so that it can be automatically registered and discovered by eureka. The home page adds eureka client dependencies to pom.xml:

Org.springframework.cloud spring-cloud-starter-netflix-eureka-client

Then add the @ EnableDiscoveryClient annotation to the Application class:

@ EnableDiscoveryClient@SpringBootApplicationpublic class Application {public static void main (String [] args) {SpringApplication.run (Application.class, args);}}

Finally, we create a class to test whether the service has been successfully registered and discovered. Create a new Java class cn.zxuqian.controllers.ServiceInstanceController and add the following code:

Package cn.zxuqian.controllers;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.cloud.client.ServiceInstance;import org.springframework.cloud.client.discovery.DiscoveryClient;import org.springframework.web.bind.annotation.PathVariable;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController;import java.util.List;@RestControllerpublic class ServiceInstanceController {@ Autowired private DiscoveryClient discoveryClient @ RequestMapping ("/ service-instances/ {applicationName}") public List serviceInstancesByApplicationName (@ PathVariable String applicationName) {return this.discoveryClient.getInstances (applicationName);}}

This is a normal RestController that defines a variable of type DiscoveryClient and adds the @ Autowire annotation. This annotation is a dependency injection feature provided by the Spring framework. Under Spring's context, it automatically looks for the implementation class of DiscoveryClient, in this case eureka client. Some of the features and principles of Spring will be discussed in future blog posts.

This class also defines a serviceInstancesByApplicationName method to handle / service-instances/ {applicationName} requests. The {applicationName} here matches the part of the url path after / service-instances/, and then annotates the applicationName parameter assigned to the method with @ PathVariable. For example, if you access http://localhost:8080/service-instances/web-client, the value of applicationName is web-client. The function of the method is to fetch the corresponding instance information from discoveryClient according to the value of spring.application.name. A list is returned, which is automatically converted to an array of json and returned to the browser.

test

Because both eureka server and web client need to read the configuration from the configuration service, start config-server first, then eureka-server, and finally web-client. After starting successfully, it may take more than ten seconds for eureka-server to discover and register web-client. After visiting http://localhost:8080/service-instances/web-client, you will get the following result:

{"host": "xuqians-imac", "port": 8080, "instanceInfo": {"instanceId": "xuqians-imac:web-client", "app": "WEB-CLIENT", "appGroupName": null, "ipAddr": "192.168.72.31", "sid": "na", "homePageUrl": "http://xuqians-imac:8080/","statusPageUrl":"http://xuqians-imac:8080/actuator/info","healthCheckUrl":"http://xuqians-imac:8080/actuator/health"," SecureHealthCheckUrl: null, "vipAddress": "web-client", "secureVipAddress": "web-client", "countryId": 1, "dataCenterInfo": {"@ class": "com.netflix.appinfo.InstanceInfo$DefaultDataCenterInfo", "name": "MyOwn"}, "hostName": "xuqians-imac", "status": "UP", "leaseInfo": {"renewalIntervalInSecs": 30, "durationInSecs": 90, "registrationTimestamp": 1525319124967, "lastRenewalTimestamp": 1525319124967, "evictionTimestamp": 0, "serviceUpTimestamp": 1525319124363}, "isCoordinatingDiscoveryServer": false "metadata": {"management.port": "8080"}, "lastUpdatedTimestamp": 1525319124967, "lastDirtyTimestamp": 1525319124297, "actionType": "ADDED", "asgName": null, "overriddenStatus": "UNKNOWN"}, "metadata": {"management.port": "8080"}, "uri": "http://xuqians-imac:8080","serviceId":"WEB-CLIENT","secure":false,"scheme":null}]"

Note that the configuration center service is not set to be registered and discovered by eureka server, because all the configuration files are placed in config-server, which has problems with eureka server, so if you want config-server to be automatically registered and discovered, you need to configure eureka server separately, then configure eureka's uri in config server, and set spring.cloud.config.discovery.enabled to true. It will be explained in detail when you need to use it later.

Summary

Configuring eureka server is fairly simple, just add a @ EnableEurekaServer annotation and turn off self-registration and discovery in the configuration. Then add the @ EnableDiscoveryClient annotation to the Application class of the client application.

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