Spring Cloud Tutorial Part 1: Eureka

Keywords: Programming Spring Maven Apache SpringBoot

1. Introduction to spring cloud

Spring cloud provides developers with tools to quickly build distributed systems, including configuration management, service discovery, circuit breakers, routing, micro-agents, event bus, global locks, decision campaigns, distributed sessions, and so on.It runs in a simple environment and can run on a developer's computer.Additionally, spring cloud is based on springboot, so you need to know something about springboot in development. If you don't, you can read this article: Learn springboot in 2 hours .In addition, if you are not familiar with the "Micro Service Architecture", you can learn about it through search engine search for "Micro Service Architecture".

2. Creating a Service Registration Center

Here, on the components we need to use, Spring Cloud Netflix's Eureka, Eureka is a service registration and discovery module.

2.1 First create a maven master project.

2.2 Then create two model projects: one as the service registry, Eureka Server, and the other as the Eureka Client.

The following is an example of creating a server to illustrate the creation process in detail:

Right-click Project - > Create Model - > Select spring initialir as follows:

Next - > Select cloud discovery - > Eureka server, and then proceed to the next step.

The pom.xml file for the created project is as follows:

<?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>2.1.8.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.free</groupId>
	<artifactId>eurekaserver</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>eurekaserver</name>
	<description>Demo project for Spring Boot</description>

	<properties>
		<java.version>1.8</java.version>
		<spring-cloud.version>Greenwich.SR3</spring-cloud.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-netflix-eureka-server</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>${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>

2.3 Starting a service registry requires only a comment @EnableEurekaServer, which needs to be added to the startup application class of the springboot project:

package com.free.eurekaserver;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;

@EnableEurekaServer
@SpringBootApplication
public class EurekaserverApplication {

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

}

**2.4 **eureka is a highly available component that does not have a backend cache, and after each instance is registered it needs to send a heartbeat to the registry (so it can be done in memory), and by default erureka server is also a eureka client, and a server must be specified.The configuration file appication.yml for eureka server:

server:
  port: 8761

eureka:
  instance:
    hostname: localhost
  client:
    registerWithEureka: false
    fetchRegistry: false
    serviceUrl:
          defaultZone: http://${eureka.instance.hostname}:${server.port}/eureka/

Indicate yourself as a eureka server by eureka.client.registerWithEureka:false and fetchRegistry:false.

2.5 Ereka server has an interface, start the project, open the browser access: http://localhost:8761, the interface is as follows:

No application available No service found...^^ Because of the fact that no service can be discovered without a registered service.

3. Create a service provider (eureka client)

When a client registers with a server, it provides some metadata, such as host and port, URL, home page, and so on.Eureka server receives a heartbeat message from each client instance.If the heartbeat times out, the instance is usually removed from the registered server.

The creation process is similar to that of a server, where the pom.xml is created as follows:

<?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>2.1.8.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.free</groupId>
	<artifactId>eurekaserver</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>eurekaserver</name>
	<description>Demo project for Spring Boot</description>

	<properties>
		<java.version>1.8</java.version>
		<spring-cloud.version>Greenwich.SR3</spring-cloud.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-netflix-eureka-server</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>${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>

Indicate yourself as a eurekaclient by commenting @EnableEurekaClient.

package com.free.servicehi;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;

@EnableEurekaClient
@SpringBootApplication
public class ServiceHiApplication {

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

}

package com.free.servicehi.web;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

/**
 * @program: SpringCloudDemo
 * @description:
 * @author: Mr.Zhou
 * @create: 2019-09-25 08:2019:26
 **/
@RestController
public class HelloController {

    @Value("${server.port}")
    String port;
    @RequestMapping("/hi")
    public String home(@RequestParam String name) {
        return "hi "+name+",i am from port:" +port;
    }

}

It is not enough to just @EnableEurekaClient. You also need to specify the address of your service registry in the configuration file, which is as follows:

server:
  port: 8762

spring:
  application:
    name: service-hi

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/

It is important to specify spring.application.name, which is the basis for subsequent calls between services.Start the project and open http://localhost:8761, the address of eureka server:

You will find a service registered with the service, named SERVICE-HI, with port 7862

Open http://localhost:8762/hi?name=zz and you will see:

hi zz,i am from port:8762

Source download: https://github.com/forezp/SpringCloudLearning/tree/master/chapter1

4. References

Official document for springcloud eureka server

Official document for springcloud eureka client

Good articles recommend:

[The simplest SpringCloud tutorial ever Final Chapter] (http://blog.csdn.net/forezp/article/details/70148833)
[The simplest SpringCloud tutorial ever Article 1: Registration and Discovery of Services (Eureka)] (http://blog.csdn.net/forezp/article/details/696915)
[The simplest SpringCloud tutorial ever Article 7: Highly Available Distributed Config (http://blog.csdn.net/forezp/article/details/70037513)

Posted by curioadmin on Tue, 24 Sep 2019 18:52:16 -0700

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