2nd/10_Wiki/Topics/Frontend/Server Side Rendering (SSR).md

---
id: wiki-2026-0508-server-side-rendering-ssr
title: Server Side Rendering (SSR)
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [SSR, Server Rendering, isomorphic rendering]
duplicate_of: none
source_trust_level: A
confidence_score: 0.95
verification_status: applied
tags: [ssr, react, nextjs, rendering, performance]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: TypeScript
  framework: Next.js 15 / React 19
---

# Server Side Rendering (SSR)

## 매 한 줄
> **"매 SSR 은 server 에서 HTML 을 생성해 first paint 를 빠르게, SEO 를 가능하게"**. 2026 기준 React 19 의 streaming SSR + Suspense + Server Components 가 표준. 매 trade-off 는 server compute cost vs CSR-only 의 blank-screen 제거. 매 modern 변형: SSG (build-time), ISR (revalidate), PPR (Partial Prerender).

## 매 핵심

### 매 rendering modes
- **CSR**: 매 client only — slow first paint, no SEO without JS
- **SSR**: 매 server-render full HTML per request
- **SSG**: 매 build-time HTML (static)
- **ISR**: 매 SSG + on-demand or time-based revalidation
- **PPR**: 매 partial prerender — static shell + dynamic holes (Next.js 15)

### 매 hydration
- Server HTML 송신 → client JS 가 attach (event handler 연결)
- Streaming SSR: HTML 을 chunk 로 진행 송신
- Selective hydration: visible / interacted 부분 우선

### 매 응용
1. Marketing / blog (SEO + fast paint).
2. E-commerce PDP (per-user pricing + SEO).
3. Dashboard shells (PPR — static shell + dynamic data).

## 💻 패턴

### Next.js 15 RSC + streaming
```tsx
// app/page.tsx
import { Suspense } from "react";
import { ProductGrid } from "./product-grid";

export default function Page() {
  return (
    <main>
      <h1>Products</h1>
      <Suspense fallback={<div>매 loading…</div>}>
        <ProductGrid />
      </Suspense>
    </main>
  );
}

// app/product-grid.tsx (RSC, runs on server)
import { db } from "@/lib/db";

export async function ProductGrid() {
  const products = await db.product.findMany({ take: 20 });
  return (
    <ul>
      {products.map((p) => <li key={p.id}>{p.name}</li>)}
    </ul>
  );
}
```

### Partial Prerendering (PPR)
```tsx
// app/dashboard/page.tsx
export const experimental_ppr = true;

import { Suspense } from "react";
import { StaticHeader } from "./header";
import { LiveMetrics } from "./metrics";

export default function Page() {
  return (
    <>
      <StaticHeader />  {/* prerendered */}
      <Suspense fallback={<MetricsSkeleton />}>
        <LiveMetrics />  {/* dynamic, streamed */}
      </Suspense>
    </>
  );
}
```

### ISR with revalidate
```tsx
// app/posts/[slug]/page.tsx
export const revalidate = 60;  // every 60s

export default async function Page({
  params,
}: { params: Promise<{ slug: string }> }) {
  const { slug } = await params;
  const post = await fetch(`https://api.example.com/posts/${slug}`,
    { next: { revalidate: 60, tags: [`post:${slug}`] } }).then((r) => r.json());
  return <article>{post.title}</article>;
}
```

### On-demand revalidation
```typescript
// app/api/revalidate/route.ts
import { revalidateTag } from "next/cache";

export async function POST(req: Request) {
  const { tag } = await req.json();
  revalidateTag(tag);
  return Response.json({ ok: true });
}
```

### Pure React 19 streaming SSR
```typescript
// server.ts
import { renderToReadableStream } from "react-dom/server";
import App from "./App";

export default async function handler(req: Request): Promise<Response> {
  const stream = await renderToReadableStream(<App url={req.url} />, {
    bootstrapModules: ["/client.js"],
    onError: (err) => console.error(err),
  });
  await stream.allReady;  // remove for true streaming
  return new Response(stream, {
    headers: { "content-type": "text/html" },
  });
}
```

### Client hydration entry
```typescript
// client.ts
import { hydrateRoot } from "react-dom/client";
import App from "./App";

hydrateRoot(document, <App url={location.href} />);
```

### Cache headers for SSR
```typescript
// app/api/data/route.ts
export async function GET() {
  return Response.json(
    { data: 42 },
    {
      headers: {
        "Cache-Control": "public, s-maxage=60, stale-while-revalidate=300",
      },
    },
  );
}
```

### Server-only utility
```typescript
// lib/server-only.ts
import "server-only";  // 매 import in client component throws

import { db } from "./db";

export async function loadSecret() {
  return db.secret.findFirst();
}
```

### Edge runtime SSR
```typescript
// app/page.tsx
export const runtime = "edge";

export default async function Page() {
  const data = await fetch("https://api.example.com/edge").then((r) => r.json());
  return <pre>{JSON.stringify(data)}</pre>;
}
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Static marketing page | SSG (`generateStaticParams`) |
| Per-user dynamic | SSR / RSC |
| Mostly static + small dynamic | **PPR** |
| Data refreshes minutes-scale | ISR with revalidate |
| Internal app, no SEO | CSR (Vite SPA) sufficient |
| Low latency global | Edge runtime SSR |

**기본값**: Next.js 15 App Router + RSC + Suspense streaming + PPR where applicable.

## 🔗 Graph
- 부모: [[Rendering Strategies]] · [[Web Performance]]
- 변형: [[CSR]] · [[SSG]] · [[ISR]] · [[Streaming SSR]]
- 응용: [[Remix]] · [[SvelteKit]] · [[Nuxt]]
- Adjacent: [[React Server Components]] · [[Hydration]] · [[Suspense]]

## 🤖 LLM 활용
**언제**: rendering strategy 결정, SEO + first paint 최적화, RSC + Suspense 설계.
**언제 X**: 매 internal admin tool with auth-only access (CSR 충분), 매 매우 dynamic real-time app (WebSocket-driven).

## ❌ 안티패턴
- **SSR everything**: 매 unnecessary server compute. 매 marketing page → SSG.
- **No streaming**: 매 await all data → blank for 5s. 매 Suspense + streaming.
- **Hydration mismatch**: server `Date.now()` vs client → 매 warning. `suppressHydrationWarning` 또는 client-only render.
- **Secret in client component**: 매 env var leak. `server-only` import.
- **Massive RSC payload**: 매 props 에 huge JSON. 매 boundary 재설계.
- **Forgetting cache tags**: ISR 인데 invalidation 못 함.

## 🧪 검증 / 중복
- Verified (Next.js 15 docs, React 19 docs, Vercel blog 2026).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — SSR full content |