服务发现与注册：Eureka与Nacos

概述

服务发现是微服务架构的核心组件。本教程介绍Eureka和Nacos的使用。

1. Eureka

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

@SpringBootApplication
@EnableEurekaServer
public class EurekaServerApplication {
    public static void main(String[] args) {
        SpringApplication.run(EurekaServerApplication.class, args);
    }
}

// Eureka Client
import org.springframework.cloud.netflix.eureka.EnableDiscoveryClient;

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

// 配置
# application.yml
eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka/
  instance:
    prefer-ip-address: true

2. Nacos

// Nacos Server
// 启动Nacos服务器
// sh startup.sh -m standalone

// Nacos Client
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;

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

// 配置
# application.yml
spring:
  cloud:
    nacos:
      discovery:
        server-addr: localhost:8848
      config:
        server-addr: localhost:8848
        file-extension: yaml

3. 实际应用示例

服务调用

import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.discovery.DiscoveryClient;
import org.springframework.stereotype.Service;

@Service
public class ServiceDiscoveryService {
    private final DiscoveryClient discoveryClient;
    
    public ServiceDiscoveryService(DiscoveryClient discoveryClient) {
        this.discoveryClient = discoveryClient;
    }
    
    public ServiceInstance getServiceInstance(String serviceName) {
        List<ServiceInstance> instances = discoveryClient.getInstances(serviceName);
        if (instances.isEmpty()) {
            throw new RuntimeException("服务不可用: " + serviceName);
        }
        return instances.get(0);
    }
    
    public String getServiceUrl(String serviceName) {
        ServiceInstance instance = getServiceInstance(serviceName);
        return instance.getUri().toString();
    }
}

配置管理

import org.springframework.beans.factory.annotation.Value;
import org.springframework.cloud.context.config.annotation.RefreshScope;
import org.springframework.stereotype.Component;

@Component
@RefreshScope
public class DynamicConfig {
    @Value("${app.feature.enabled:false}")
    private boolean featureEnabled;
    
    @Value("${app.config.value:default}")
    private String configValue;
    
    public boolean isFeatureEnabled() {
        return featureEnabled;
    }
    
    public String getConfigValue() {
        return configValue;
    }
}

4. 最佳实践

1. 选择合适的服务发现工具：Eureka简单，Nacos功能丰富
2. 健康检查：确保服务可用性
3. 负载均衡：使用Ribbon或LoadBalancer
4. 配置管理：使用配置中心统一管理配置
5. 监控告警：监控服务状态

总结

服务发现是微服务架构的核心组件。掌握Eureka和Nacos的使用，可以构建可扩展、高可用的微服务系统。