2nd/10_Wiki/Topics/AI_and_ML/Client-Server Architecture Pattern.md

id, title, category, status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, verification_status, tags, raw_sources, last_reinforced, github_commit, tech_stack

id	title	category	status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	verification_status	tags	raw_sources	last_reinforced	github_commit	tech_stack
wiki-2026-0508-client-server	Client-Server Architecture Pattern	10_Wiki/Topics	verified	self	client-server REST gRPC HTTP web architecture centralized model two-tier three-tier	none	A	0.95	applied	architecture client-server rest grpc http network web-development scalability		2026-05-10	pending	language framework language-agnostic HTTP / REST / gRPC / WebSocket

Client-Server Architecture

📌 한 줄 통찰

"매 자원 의 request ↔ provider". 매 dominant network model. 매 single point of failure 가, 매 scale + control 의 huge. 매 modern: 매 BFF, 매 edge, 매 multi-region, 매 P2P 와 의 hybrid.

매 핵심

매 components

• Client: 매 UI + 매 request.
• Server: 매 logic + 매 data.
• Network protocol: HTTP, gRPC, WebSocket, MQTT.

매 tier

• Two-tier: client + DB.
• Three-tier: client + app server + DB.
• N-tier: client + BFF + microservices + DB + cache.

매 protocol comparison

Protocol	Use case	Latency	Streaming
REST/HTTP	General CRUD	mid	✗
gRPC	Internal RPC	low	✓ (bidirectional)
GraphQL	Flexible query	mid	partial (subscription)
WebSocket	Real-time	very low	✓
Server-Sent Events	Server → Client	low	✓ (one-way)
MQTT	IoT, low-bandwidth	low	✓
WebRTC	P2P media	very low	✓

매 advantages

• 매 centralized control.
• 매 division of labor.
• 매 independent update.
• 매 scale (server-side).
• 매 strong security (server-side).

매 disadvantages

• 매 single point of failure.
• 매 network dependency.
• 매 latency.
• 매 cost (server infra).
• 매 scaling complexity.

매 alternative / hybrid

• P2P (BitTorrent, IPFS): 매 decentralized.
• Edge computing: 매 close to user.
• Serverless: 매 ephemeral.
• CRDT + 매 sync: 매 offline-first.
• Local-first (Ink & Switch).

매 modern pattern

BFF (Backend for Frontend)

• 매 mobile / web 별 API.
• 매 client-specific aggregation.

API Gateway

• 매 single entry.
• 매 auth / rate / route.

Service Mesh

• 매 inter-service communication.
• 매 Istio, Linkerd.

CDN / Edge

• 매 static content.
• 매 closer to user.
• 매 Cloudflare Workers, Vercel Edge.

Multi-region

• 매 active-active.
• 매 latency 의 minimize.

💻 패턴

REST API (Express)

import express from 'express';
const app = express();

app.use(express.json());

app.get('/users/:id', async (req, res) => {
  const user = await db.users.findById(req.params.id);
  if (!user) return res.status(404).json({ error: 'Not found' });
  res.json(user);
});

app.post('/users', async (req, res) => {
  const user = await db.users.create(req.body);
  res.status(201).json(user);
});

app.listen(3000);

gRPC (proto + server)

// user.proto
service UserService {
  rpc GetUser(GetUserRequest) returns (User);
  rpc StreamUsers(stream UserFilter) returns (stream User);
}

message GetUserRequest { string id = 1; }
message User { string id = 1; string email = 2; }

import * as grpc from '@grpc/grpc-js';

const server = new grpc.Server();
server.addService(UserService, {
  getUser: async (call, callback) => {
    const user = await db.users.findById(call.request.id);
    callback(null, user);
  },
});
server.bindAsync('0.0.0.0:50051', grpc.ServerCredentials.createInsecure(), () => server.start());

WebSocket (real-time)

import { WebSocketServer } from 'ws';

const wss = new WebSocketServer({ port: 8080 });
wss.on('connection', (ws) => {
  ws.on('message', (data) => {
    // 매 broadcast
    wss.clients.forEach(c => c.readyState === 1 && c.send(data));
  });
});

Server-Sent Events

app.get('/events', (req, res) => {
  res.set({
    'Content-Type': 'text/event-stream',
    'Cache-Control': 'no-cache',
    'Connection': 'keep-alive',
  });
  
  const interval = setInterval(() => {
    res.write(`data: ${JSON.stringify({ time: Date.now() })}\n\n`);
  }, 1000);
  
  req.on('close', () => clearInterval(interval));
});

Three-tier deployment

# docker-compose.yml
services:
  client:
    image: my-frontend:latest
    ports: ['80:80']
  
  api:
    image: my-api:latest
    environment:
      - DATABASE_URL=postgres://db:5432/app
      - REDIS_URL=redis://cache:6379
    deploy:
      replicas: 3
  
  cache:
    image: redis:7
  
  db:
    image: postgres:16
    volumes: ['./data:/var/lib/postgresql/data']

API Gateway (Kong / Express middleware)

// 매 simple gateway middleware
import rateLimit from 'express-rate-limit';
import jwt from 'jsonwebtoken';

app.use(rateLimit({ windowMs: 60_000, max: 100 }));

app.use((req, res, next) => {
  const token = req.headers.authorization?.split(' ')[1];
  if (!token) return res.status(401).end();
  try {
    req.user = jwt.verify(token, process.env.JWT_SECRET!);
    next();
  } catch {
    res.status(401).end();
  }
});

app.use('/api/users', proxy('http://user-service:3001'));
app.use('/api/orders', proxy('http://order-service:3002'));

BFF (TypeScript)

// 매 mobile-specific endpoint
app.get('/mobile/dashboard', async (req, res) => {
  const [user, recent_orders, notifications] = await Promise.all([
    userService.get(req.user.id),
    orderService.recent(req.user.id, 5),
    notificationService.unread(req.user.id),
  ]);
  
  // 매 mobile-friendly aggregate
  res.json({
    user: { id: user.id, name: user.name },
    recent: recent_orders.map(o => ({ id: o.id, total: o.total })),
    badge_count: notifications.length,
  });
});

Edge Function (Cloudflare Workers)

export default {
  async fetch(request, env) {
    const url = new URL(request.url);
    
    // 매 edge cache
    const cache = caches.default;
    const cached = await cache.match(request);
    if (cached) return cached;
    
    // 매 origin fetch
    const response = await fetch(`https://origin.example.com${url.pathname}`);
    
    // 매 cache
    response.headers.set('Cache-Control', 'public, max-age=60');
    await cache.put(request, response.clone());
    return response;
  },
};

Health check + circuit breaker

app.get('/health', (req, res) => {
  const checks = {
    db: db.isConnected(),
    redis: redis.ping(),
    deps: externalApi.healthy(),
  };
  
  if (Object.values(checks).every(v => v)) {
    res.json({ status: 'ok', checks });
  } else {
    res.status(503).json({ status: 'degraded', checks });
  }
});

🤔 결정 기준

상황	Pattern
Web app	Three-tier + REST
Internal services	gRPC + service mesh
Real-time	WebSocket / SSE
IoT	MQTT
Mobile	REST + BFF
Offline-first	CRDT sync + local-first
Cross-region read	Edge + CDN
P2P file	BitTorrent / IPFS
Heavy media	WebRTC

기본값: REST + 3-tier. 매 internal = gRPC. 매 real-time = WebSocket.

🔗 Graph

• 부모: Software Architecture Styles · Distributed-Systems
• 변형: REST · gRPC · MQTT · WebRTC
• 응용: BFF · API-Gateway · Service Mesh · Edge Computing
• 대안: Local-First · Serverless · CRDT
• Adjacent: CAP-Theorem · Availability-and-Persistence · Microservices

🤖 LLM 활용

언제: 매 system design. 매 protocol decision. 매 architecture review. 매 onboarding. 언제 X: 매 single-machine app. 매 P2P-only domain.

❌ 안티패턴

• Single-point-of-failure 무시: 매 multi-AZ 의 X.
• Chatty client (N+1): 매 BFF 의 lieu.
• Synchronous chain (5+ hop): 매 cascading failure.
• No rate limit: 매 abuse vulnerability.
• REST on real-time: 매 polling overhead.
• gRPC for browser: 매 매 gateway 필요.
• No health check: 매 silent degradation.

🧪 검증 / 중복

• Verified (Roy Fielding REST thesis, gRPC docs, BFF pattern Sam Newman).
• 신뢰도 A.
• Related: Software Architecture Styles · Microservices · CAP-Theorem · Bounded Contexts (DDD) · Availability-and-Persistence.

🕓 Changelog

날짜	변경
2026-05-08	Phase 1
2026-05-10	Manual cleanup — protocol matrix + tier + modern patterns + 매 Express / gRPC / WS / Edge code