---
id: wiki-2026-0508-saas-software-as-a-service
title: SaaS (Software as a Service)
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [Software as a Service, Multi-tenant SaaS, Cloud Software]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [business-model, cloud, multi-tenant, devops]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: typescript
  framework: stripe-postgres
---

# SaaS (Software as a Service)

## 매 한 줄
> **"매 software 의 매 product 가 매 service 가 된다"**. SaaS 는 매 vendor-hosted 매 multi-tenant application 의 매 subscription 으로 매 deliver — 매 install 없음, 매 patch 없음, 매 elastic. Salesforce(1999) 가 매 시작, 2026 현재 매 vertical SaaS (industry-specific) 가 매 horizontal 을 매 outpace; 매 AI-native SaaS (Cursor, Linear AI) 가 매 per-seat → 매 outcome-based pricing 으로 매 transition 중.

## 매 핵심

### 매 Architecture archetypes
- **Pool model**: 매 single DB, 매 tenant_id column. 매 cheapest, 매 noisy-neighbor risk.
- **Bridge model**: 매 schema-per-tenant. 매 isolation 좋음, 매 migration 복잡.
- **Silo model**: 매 DB-per-tenant. 매 max isolation, 매 expensive.
- **Hybrid**: free tier pool, enterprise silo.

### 매 Economics
- **MRR/ARR**: monthly/annual recurring revenue.
- **Churn**: gross (lost) vs net (incl. expansion).
- **CAC payback**: < 12 months 매 healthy.
- **NRR (Net Revenue Retention)**: > 110% 매 best-in-class.

### 매 응용
1. CRM (Salesforce, HubSpot).
2. Dev tools (GitHub, Vercel).
3. Vertical (Toast — restaurant, Veeva — pharma).
4. AI-native (Cursor, Granola, Linear).

## 💻 패턴

### Tenant isolation (Postgres RLS)
```sql
CREATE TABLE invoices (
  id uuid PRIMARY KEY,
  tenant_id uuid NOT NULL,
  amount_cents integer NOT NULL
);
ALTER TABLE invoices ENABLE ROW LEVEL SECURITY;
CREATE POLICY tenant_isolation ON invoices
  USING (tenant_id = current_setting('app.current_tenant')::uuid);

-- Per-request
SET LOCAL app.current_tenant = 'abc-123';
SELECT * FROM invoices; -- only abc-123's rows
```

### Stripe subscription webhook
```typescript
import Stripe from "stripe";
const stripe = new Stripe(process.env.STRIPE_KEY!);

app.post("/webhook", async (req, res) => {
  const event = stripe.webhooks.constructEvent(
    req.rawBody, req.headers["stripe-signature"]!, process.env.STRIPE_WH_SECRET!
  );
  switch (event.type) {
    case "customer.subscription.updated":
      await db.tenant.update({
        where: { stripeCustomerId: event.data.object.customer },
        data: { plan: event.data.object.items.data[0].price.lookup_key },
      });
      break;
    case "customer.subscription.deleted":
      await scheduleTenantOffboarding(event.data.object.customer);
      break;
  }
  res.json({ received: true });
});
```

### Feature flag per plan
```typescript
const PLAN_FEATURES = {
  free: ["basic_export"],
  pro: ["basic_export", "api_access", "sso"],
  enterprise: ["basic_export", "api_access", "sso", "audit_log", "custom_domain"],
};
function hasFeature(tenant: Tenant, feature: string): boolean {
  return PLAN_FEATURES[tenant.plan]?.includes(feature) ?? false;
}
```

### Usage metering (event-based)
```typescript
async function recordUsage(tenantId: string, metric: string, qty: number) {
  await db.usageEvent.create({ data: { tenantId, metric, qty, ts: new Date() } });
  await stripe.subscriptionItems.createUsageRecord(
    tenant.stripeSubItemId,
    { quantity: qty, timestamp: Math.floor(Date.now() / 1000), action: "increment" }
  );
}
```

### Per-tenant rate limit
```typescript
import { Ratelimit } from "@upstash/ratelimit";
const limiters = new Map<string, Ratelimit>();
function getLimiter(tenant: Tenant) {
  const limit = tenant.plan === "enterprise" ? 1000 : 100;
  if (!limiters.has(tenant.id)) {
    limiters.set(tenant.id, new Ratelimit({
      redis, limiter: Ratelimit.slidingWindow(limit, "1 m"),
    }));
  }
  return limiters.get(tenant.id)!;
}
```

## 매 결정 기준
| 상황 | Tenancy model |
|---|---|
| 매 SMB, 매 < $50 ARR / tenant | Pool (RLS) |
| 매 mid-market | Bridge (schema-per) |
| 매 enterprise, 매 compliance | Silo (DB-per or single-tenant cluster) |
| 매 AI inference heavy | Pool + per-tenant queue |

**기본값**: Pool with RLS, escape-hatch to silo for enterprise.

## 🔗 Graph
- 부모: [[Cloud Computing]] · [[Business_Strategy]]
- 변형: [[PaaS]] · [[IaaS]] · [[Vertical SaaS]]
- 응용: [[Cloud_Native]] · [[Multi-tenant Architecture]]
- Adjacent: [[Stripe Billing]] · [[Feature-Flags]]

## 🤖 LLM 활용
**언제**: Onboarding email personalization, churn-risk classification from usage signals, customer success summary, AI copilot as product feature.
**언제 X**: 매 contract pricing — human sales.

## ❌ 안티패턴
- **No tenant_id**: 매 cross-tenant data leak — 매 existential.
- **Single noisy tenant**: 매 1 enterprise = 매 80% load → 매 SLO collapse for all. 매 tier-isolate.
- **Free forever**: 매 conversion 0% → 매 unit economics 의 매 broken.
- **Hand-rolled billing**: edge case 의 매 hell. Stripe / Lago / Orb 의 매 사용.

## 🧪 검증 / 중복
- Verified (AWS SaaS Lens 2024, OpenView SaaS Benchmarks, Tomasz Tunguz reports).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — multi-tenant + AI-native SaaS 2026 |