Nacos 注册中心

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

@RestController
@RequestMapping("/user")
public class UserController {

    @Value("${server.port}")
    private String port;

    @GetMapping("/{id}")
    public String getUser(@PathVariable Long id) {
        return "User-" + id + " from port: " + port;
    }
}

@Configuration
public class RestTemplateConfig {

    @Bean
    @LoadBalanced    // 核心：开启负载均衡 + 服务名解析
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

@RestController
@RequestMapping("/order")
public class OrderController {

    @Autowired
    private RestTemplate restTemplate;

    @GetMapping("/{id}")
    public String getOrder(@PathVariable Long id) {
        // 使用服务名替代 IP:Port，Nacos + LoadBalancer 自动解析
        String url = "http://user-service/user/" + id;
        return restTemplate.getForObject(url, String.class);
    }
}

// 订单服务中定义的用户服务调用接口
@FeignClient(name = "user-service", path = "/user")
public interface UserFeignClient {

    @GetMapping("/{id}")
    String getUser(@PathVariable("id") Long id);
}

@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients    // 激活 Feign 客户端扫描
public class OrderServiceApplication {
    public static void main(String[] args) {
        SpringApplication.run(OrderServiceApplication.class, args);
    }
}

@RestController
@RequestMapping("/order")
public class OrderController {

    @Autowired
    private UserFeignClient userFeignClient;

    @GetMapping("/{id}")
    public String getOrder(@PathVariable Long id) {
        // 像调用本地方法一样调用远程服务，底层自动通过 Nacos 发现实例
        String userInfo = userFeignClient.getUser(id);
        return "Order-" + id + " | " + userInfo;
    }
}

@Configuration
public class GrayLoadBalancerConfig {

    @Bean
    public ReactorLoadBalancer<ServiceInstance> grayLoadBalancer(
            Environment env,
            LoadBalancerClientFactory factory) {
        String serviceName = env.getProperty(LoadBalancerClientFactory.PROPERTY_NAME);
        return new GrayLoadBalancer(
            factory.getLazyProvider(serviceName, ServiceInstanceListSupplier.class),
            serviceName
        );
    }
}

// 灰度负载均衡器核心逻辑
public class GrayLoadBalancer implements ReactorServiceInstanceLoadBalancer {

    private final ObjectProvider<ServiceInstanceListSupplier> serviceInstanceListSupplierProvider;
    private final String serviceName;

    @Override
    public Mono<Response<ServiceInstance>> choose(Request request) {
        ServiceInstanceListSupplier supplier =
            serviceInstanceListSupplierProvider.getIfAvailable();
        return supplier.get()
            .next()
            .map(instances -> {
                // 从请求上下文中获取灰度标记
                RequestDataContext context = (RequestDataContext) request.getContext();
                String version = context.getClientRequest()
                    .getHeaders()
                    .getFirst("version");
                // 按版本过滤实例
                List<ServiceInstance> matched = instances.stream()
                    .filter(i -> version == null ||
                        version.equals(i.getMetadata().get("version")))
                    .collect(Collectors.toList());
                if (matched.isEmpty()) {
                    // 回退到默认实例
                    matched = instances;
                }
                ServiceInstance instance = matched.get(
                    ThreadLocalRandom.current().nextInt(matched.size()));
                return new DefaultResponse(instance);
            });
    }
}