spring cloud（Greenwich SR）- Eureka

Posted 2022-01-01 amberbar

spring cloud study

本次学习基于spring cloud Greenwich SR1 版本

学习要点:

Spring Boot/Spring Cloud应用开发套路

• 加依赖
• 加注解
• 写配置

Eureka (服务注册与发现)

Eureka是Netflix开源的服务发现组件，本身是一个基于REST的服务，包含Server和Client两部分，Spring Cloud将它集成在子项目Spring Cloud Netflix中

Eureka Server (快速入门)

遵循开发套路

• 添加依赖

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

• 添加注解 @EnableEurekaServer

@SpringBootApplication
@EnableEurekaServer 
public class EurekaApplication 

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

server:
  port: 8001

spring:
  application:
    name: microservice-discovery-eureka

eureka:
  client:
    service-url:
      #erueka server的地址，记住/eureka不要掉了
      defaultZone: http://localhost:8001/eureka
    # 是否从eureka server注册，这里我们选择false
    fetch-registry: false
    # 是否从eureka server 中拉取服务
    register-with-eureka: false

启动项目,访问http://localhost:8001/

Eureka Client

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

@SpringBootApplication
@EnableDiscoveryClient
public class ProvideApplication 

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

在Greenwich SR1版本中可以省略@EnableEurekaClient和@EnableDiscoveryClient注解，但为了养成好习惯，建议加上相应注解

@EnableDiscoveryClient: 可以配合不同的服务发现server 使用
@EnableEurekaClient: 只能配合 Eureka server 使用

server:
  port: 9001
spring:
  application:
    name: microservice-provide-user
  datasource:
    driverClassName: com.mysql.jdbc.Driver
    url: jdbc:mysql://localhost:3306/cloud-study?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true&useSSL=false&allowMultiQueries=true
    username: root
    password: root
    jpa:
      hibernate:
        ddl-auto: update
      show-sql: true


eureka:
  client:
    service-url:
      defaultZone: http://localhost:8001/eureka/
  instance:
   # 是否显示ip,如果不设置那么就会显示主机名，默认false
    prefer-ip-address: true

启动项目，可以发现项目已经被注册进eureka

完整代码：

microservice-discovery-eureka

microservice-provide-user

### eureka 深入

Eureka包含两个组件：Eureka Server 和 Eureka Client:

• Eureka Server负责提供服务发现的能力，各个微服务启动时，会向Eureka Server注册自己的信息（例如IP、端口、微服务名称等）
• Eureka Client是一个Java客户端，可以与EurekaServer交互
• client启动后，会周期性的像server发送心跳，默认情况下 30s,如果server在一定时间内没有收到client的心跳，那么server会注销实例90s
• Eureka Server遵循CAP原则，符合AP。eureka集群中每个节点之间都是平等状态。如果一个节点宕机，不会进行选举。因此可以很有效的保证可用性

搭建erueka集群

在host中添加
127.0.0.1 peer1 peer2
可以再microservice-discovery-eureka 的基础上修改application.yml

spring:
  application:
    name: microservice-discovery-eureka-cluster
eureka:
  client:
    serviceUrl:
      defaultZone: http://peer2:8002/eureka/,http://peer1:8003/eureka/
---
spring:
  profiles: peer1
server:
  port: 8002
eureka:
  instance:
    hostname: peer1
---
spring:
  profiles: peer2
server:
  port: 8003
eureka:
  instance:
    hostname: peer2

修改microservice-provide-user的application.yml

server:
  port: 9002
spring:
  application:
    name: microservice-provide-user
  datasource:
    driverClassName: com.mysql.jdbc.Driver
    url: jdbc:mysql://localhost:3306/cloud-study?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true&useSSL=false&allowMultiQueries=true
    username: root
    password: root
    jpa:
      show-sql: true
eureka:
  client:
    service-url:
      defaultZone: http://peer1:8002/eureka/,http://peer2:8003/eureka/
  instance:
    prefer-ip-address: true

启动服务