2nd/10_Wiki/Topics/Architecture/API-First_Architecture.md

---
id: wiki-2026-0508-api-first-architecture
title: API-First Architecture
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [API-first design, Contract-first, Schema-first]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [architecture, api, openapi, contract-first, design]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: yaml
  framework: OpenAPI 3.1, Stoplight, Spectral, buf
---

# API-First Architecture

## 매 한 줄
> **"매 API spec 의 first artifact — code follows contract"**. 매 design-first → spec → mock → impl 매 separate workflow. 매 Swagger (2010) → OpenAPI 3.0 (2017) → 3.1 (2021, JSON Schema 2020-12 align) → AsyncAPI 2.6/3.0 (events) → buf (gRPC). 매 2026 modern stack 은 spec-driven codegen + lint (Spectral) + breaking change detection (buf, oasdiff) + AI-assisted spec (Claude Opus 4.7).

## 매 핵심

### 매 workflow
1. **Design**: write OpenAPI/proto spec 매 먼저.
2. **Review**: stakeholders (FE/BE/partner) review spec, not code.
3. **Mock**: Prism/Stoplight serve mock from spec.
4. **Generate**: SDK (oapi-codegen, openapi-typescript), server stubs.
5. **Implement**: fill stubs, validate at runtime.
6. **Test**: contract tests against spec.
7. **Govern**: lint (Spectral), diff (oasdiff), versioning.

### 매 vs code-first
- **Code-first**: write handler → annotate → generate spec. Drift risk, late stakeholder feedback.
- **API-first**: write spec → generate handler → fill. Single source of truth.

### 매 응용
1. **Public SaaS API** — Stripe-style spec-driven.
2. **Multi-platform SDK distribution** — auto-generated TS/Python/Go/Java clients.
3. **Frontend/backend parallel dev** — FE works against mock from day 1.
4. **B2B integration contracts** — partners review spec before impl.

## 💻 패턴

### OpenAPI 3.1 spec
```yaml
openapi: 3.1.0
info: { title: Orders API, version: 1.0.0 }
paths:
  /orders/{id}:
    get:
      operationId: getOrder
      parameters:
        - { name: id, in: path, required: true, schema: {type: string} }
      responses:
        "200":
          description: OK
          content:
            application/json:
              schema: { $ref: "#/components/schemas/Order" }
        "404": { $ref: "#/components/responses/NotFound" }
components:
  schemas:
    Order:
      type: object
      required: [id, status]
      properties:
        id: { type: string, format: uuid }
        status: { type: string, enum: [pending, paid, shipped] }
        total: { type: number, minimum: 0 }
```

### Mock server (Prism)
```bash
npx @stoplight/prism-cli mock spec.yaml --port 4010
# Now FE devs hit http://localhost:4010/orders/123 with realistic responses
```

### Spectral lint config
```yaml
# .spectral.yaml
extends: [[spectral:oas, all]]
rules:
  operation-operationId-unique: error
  operation-tag-defined: error
  no-eval-in-markdown: error
  custom-versioned-path:
    given: "$.paths"
    severity: error
    then:
      function: pattern
      functionOptions: { match: "^/v\\d+/" }
```

### Type-safe client (openapi-typescript)
```bash
npx openapi-typescript spec.yaml -o src/api-types.ts
```
```typescript
import createClient from "openapi-fetch";
import type { paths } from "./api-types";

const client = createClient<paths>({ baseUrl: "https://api.example.com" });
const { data, error } = await client.GET("/orders/{id}", {
  params: { path: { id: "abc" } },
});
// data: Order | undefined, fully typed
```

### Server stub (oapi-codegen, Go)
```bash
oapi-codegen -package api -generate types,server spec.yaml > api/api.gen.go
```
```go
type ServerImpl struct{ db *sql.DB }
func (s *ServerImpl) GetOrder(c echo.Context, id string) error {
    var o Order
    if err := s.db.QueryRow("SELECT ...").Scan(...); err != nil { ... }
    return c.JSON(200, o)
}
```

### Breaking change detection (oasdiff)
```bash
oasdiff breaking spec-v1.yaml spec-v2.yaml --fail-on ERR
# CI gate: blocks PR if breaking change without major version bump
```

### AsyncAPI for events
```yaml
asyncapi: 3.0.0
info: { title: Orders Events, version: 1.0.0 }
channels:
  orderCreated:
    address: orders.created
    messages:
      OrderCreatedMessage:
        payload:
          $ref: "#/components/schemas/Order"
operations:
  publishOrderCreated:
    action: send
    channel: { $ref: "#/channels/orderCreated" }
```

### buf for gRPC governance
```yaml
# buf.yaml
version: v2
modules:
  - path: proto
breaking:
  use: [FILE]
lint:
  use: [DEFAULT]
  except: [PACKAGE_VERSION_SUFFIX]
```

## 매 결정 기준
| 상황 | Spec |
|---|---|
| HTTP REST, public | OpenAPI 3.1 |
| Async events | AsyncAPI 3.0 |
| gRPC | proto + buf |
| GraphQL | SDL + Apollo Federation |
| Internal-only, single team | Code-first (faster iteration) |

**기본값**: 매 OpenAPI 3.1 + Spectral lint + Prism mock + openapi-typescript codegen + oasdiff CI.

## 🔗 Graph
- 부모: [[API Fundamentals]] · [[Contract-Driven Development]]
- 변형: [[Schema-First GraphQL]] · [[Proto-First gRPC]]
- 응용: [[OpenAPI]] · [[AsyncAPI]] · [[SDK Generation]]
- Adjacent: [[Consumer-Driven Contracts]] · [[Pact Testing]] · [[API Gateway]]

## 🤖 LLM 활용
**언제**: 매 multi-team API, 매 public SDK distribution, 매 partner integration, 매 FE/BE parallel dev.
**언제 X**: 매 prototype, 매 throwaway script, 매 single-developer monolith.

## ❌ 안티패턴
- **Spec-as-documentation only**: 매 not source of truth, 매 drift. 매 codegen-driven 의 enforce.
- **No CI lint**: 매 spec rot. 매 Spectral / vacuum 의 사용.
- **Big-bang spec**: 매 review fatigue. 매 incremental + path-scoped reviews.
- **No mock**: 매 FE blocked on BE. 매 Prism mock 의 day-1 deploy.

## 🧪 검증 / 중복
- Verified (OpenAPI 3.1 spec, AsyncAPI spec, Stoplight docs, buf docs, ThoughtWorks Tech Radar "Design APIs first").
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — full content (API-first workflow + tooling) |