서비스 디스커버리

Java code

import java.util.*;
import java.util.concurrent.*;

public class ServiceDiscovery {
    record ServiceInstance(String id, String host, int port, boolean healthy) {}

    // 서비스 레지스트리
    static class Registry {
        private final Map<String, List<ServiceInstance>> services =
            new ConcurrentHashMap<>();
        private int roundRobin = 0;

        // 서비스 등록
        void register(String name, ServiceInstance instance) {
            services.computeIfAbsent(name, k -> new CopyOnWriteArrayList<>())
                    .add(instance);
            System.out.printf("등록: %s -> %s:%d%n", name, instance.host(), instance.port());
        }

        // 서비스 해제
        void deregister(String name, String instanceId) {
            List<ServiceInstance> list = services.get(name);
            if (list != null) {
                list.removeIf(i -> i.id().equals(instanceId));
            }
        }

        // 서비스 발견 (라운드 로빈 로드 밸런싱)
        Optional<ServiceInstance> discover(String name) {
            List<ServiceInstance> list = services.get(name);
            if (list == null || list.isEmpty()) return Optional.empty();

            List<ServiceInstance> healthy = list.stream()
                .filter(ServiceInstance::healthy).toList();
            if (healthy.isEmpty()) return Optional.empty();

            int idx = Math.abs(roundRobin++) % healthy.size();
            return Optional.of(healthy.get(idx));
        }
    }

    public static void main(String[] args) {
        Registry registry = new Registry();
        registry.register("user-service",
            new ServiceInstance("u1", "10.0.0.1", 8080, true));
        registry.register("user-service",
            new ServiceInstance("u2", "10.0.0.2", 8080, true));

        for (int i = 0; i < 4; i++) {
            registry.discover("user-service").ifPresent(inst ->
                System.out.printf("발견: %s:%d%n", inst.host(), inst.port()));
        }
    }
}