05-LoadBalancer负载均衡

1、介绍

目前主流的负载方案分为以下两种：

• 集中式负载均衡，在消费者和服务提供方中间使用独立的代理方式进行负载，有硬件的（比如 F5），也有软件的（比如 Nginx）。
• 客户端根据自己的请求情况做负载均衡，LoadBalancer、Ribbon 就属于客户端自己做负载均衡。

2、快速开始

废话不多少，上代码。

pom.xml

maven依赖配置文件，如下：

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">	<modelVersion>4.0.0</modelVersion>	<groupId>com.mindasoft</groupId>	<artifactId>spring-cloud-ribbon-consumer</artifactId>	<version>0.0.1-SNAPSHOT</version>	<packaging>jar</packaging>	<name>spring-cloud-ribbon-consumer</name>	<description>Demo project for Spring Boot</description>	<parent>		<groupId>org.springframework.boot</groupId>		<artifactId>spring-boot-starter-parent</artifactId>		<version>2.6.4</version>		<relativePath/> <!-- lookup parent from repository -->	</parent>	<properties>		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>		<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>		<java.version>1.8</java.version>		<spring-cloud.version>2021.0.1</spring-cloud.version>	</properties>	<dependencies>		<dependency>			<groupId>org.springframework.cloud</groupId>			<artifactId>spring-cloud-starter-netflix-eureka-client</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>${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>	<repositories>		<repository>			<id>nexus-aliyun</id>			<name>Nexus aliyun</name>			<url>https://maven.aliyun.com/repository/public</url>			<layout>default</layout>			<snapshots>				<enabled>false</enabled>			</snapshots>			<releases>				<enabled>true</enabled>			</releases>		</repository>	</repositories>	<pluginRepositories>		<pluginRepository>			<id>nexus-aliyun</id>			<name>Nexus aliyun</name>			<url>https://maven.aliyun.com/repository/public</url>			<snapshots>				<enabled>false</enabled>			</snapshots>			<releases>				<enabled>true</enabled>			</releases>		</pluginRepository>	</pluginRepositories></project>

上面配置文件，我们没有新增LoadBalancer的配置，其实spring-cloud-starter-netflix-eureka-client已经依赖了一个具体实现，在老版本的是Ribbon，新的版本是Spring自己实现的loadbalancer，如下：。

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

所以不需要格外添加配置。

application.properties

服务配置文件，也可以用yml，如下：

server.port=9003# 服务注册中心地址eureka.client.service-url.defaultZone=http://localhost:9000/eureka/# 服务名称spring.application.name=loadbalancer-customer

LoadBalancerConsumerApplication

服务启动类，如下：

import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.cloud.client.discovery.EnableDiscoveryClient;import org.springframework.cloud.client.loadbalancer.LoadBalanced;import org.springframework.context.annotation.Bean;import org.springframework.web.client.RestTemplate;@EnableDiscoveryClient // Eureka Discovery Client 标识@SpringBootApplicationpublic class LoadBalancerConsumerApplication {	@Bean	@LoadBalanced  		// 开启负载均衡的功能	RestTemplate restTemplate() {		return new RestTemplate();	}	public static void main(String[] args) {		SpringApplication.run(SpringCloudRibbonConsumerApplication.class, args);	}}

上面代码中，@LoadBalanced 注解开启了RestTemplate的负载均衡，具体原理后面深入源码学习时再做了解。这里只需要了解该注解标记后，该http请求会有负载均衡效果。

ConsumerController

服务调用，

import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController;import org.springframework.web.client.RestTemplate;/** * Created by huangmin */@RestControllerpublic class ConsumerController {	private static final Logger LOGGER = LoggerFactory.getLogger(ConsumerController.class);		@Autowired	private RestTemplate restTemplate; // HTTP客户端	@RequestMapping("/hello")	public String hello() {		String providerMsg = restTemplate.getForEntity("http://PROVIDER-SERVICE/hello",				String.class).getBody();		return "Hello,I'm Customer! msg from provider : <br/><br/> " + providerMsg;	}}

3、Ribbon

如果需要使用Ribbon的话，我们只需要改一下依赖文件即可：

<dependencies>	<dependency>		<groupId>org.springframework.cloud</groupId>		<artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>		<exclusions>			<exclusion>				<groupId>org.springframework.cloud</groupId>				<artifactId>spring-cloud-loadbalancer</artifactId>			</exclusion>		</exclusions>	</dependency>	<dependency>		<groupId>org.springframework.cloud</groupId>		<artifactId>spring-cloud-starter-netflix-ribbon</artifactId>                <version>2.2.10.RELEASE</version>	</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>

这里移出了loadbalancer ，添加Ribbon的包。其他配置不用动即可换成Ribbon