"Docker 실전 — 개발자를 위한 컨테이너 가이드"

## CI/CD 파이프라인 개요

```
git push (main)
    ↓
GitHub Actions 트리거
    ↓
① 테스트 실행
    ↓
② Docker 이미지 빌드
    ↓
③ GHCR(GitHub Container Registry)에 푸시
    ↓
④ 서버에 배포 (SSH → docker compose pull && up)
```

---

## 완성형 워크플로우

```yaml
# .github/workflows/deploy.yml
name: Build & Deploy

on:
  push:
    branches: [main]
  pull_request:
    branches: [main]

env:
  REGISTRY: ghcr.io
  IMAGE_NAME: ${{ github.repository }}

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

- name: Run tests with Docker Compose
        run: |
          docker compose -f docker-compose.test.yml up --abort-on-container-exit
          docker compose -f docker-compose.test.yml down

build-push:
    needs: test
    runs-on: ubuntu-latest
    if: github.ref == 'refs/heads/main'
    permissions:
      contents: read
      packages: write

steps:
      - uses: actions/checkout@v4

- name: Log in to GHCR
        uses: docker/login-action@v3
        with:
          registry: ${{ env.REGISTRY }}
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}

- name: Extract metadata
        id: meta
        uses: docker/metadata-action@v5
        with:
          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
          tags: |
            type=sha,prefix=sha-
            type=raw,value=latest

- name: Build and push
        uses: docker/build-push-action@v5
        with:
          context: .
          push: true
          tags: ${{ steps.meta.outputs.tags }}
          cache-from: type=gha    # GitHub Actions 캐시 활용
          cache-to: type=gha,mode=max

deploy:
    needs: build-push
    runs-on: ubuntu-latest
    if: github.ref == 'refs/heads/main'

steps:
      - name: Deploy to server
        uses: appleboy/ssh-action@v1
        with:
          host: ${{ secrets.SERVER_HOST }}
          username: ${{ secrets.SERVER_USER }}
          key: ${{ secrets.SERVER_SSH_KEY }}
          script: |
            cd /app
            echo ${{ secrets.GITHUB_TOKEN }} | docker login ghcr.io -u ${{ github.actor }} --password-stdin
            docker compose pull
            docker compose up -d --no-build
            docker image prune -f
```

---

## Secrets 설정

GitHub 레포 → Settings → Secrets and variables → Actions:

| Secret | 값 |
|--------|---|
| `SERVER_HOST` | 서버 IP 또는 도메인 |
| `SERVER_USER` | SSH 사용자 (예: ubuntu) |
| `SERVER_SSH_KEY` | SSH 개인키 (`cat ~/.ssh/id_rsa`) |

`GITHUB_TOKEN`은 자동으로 제공되므로 별도 설정 불필요.

---

## 테스트용 Compose

```yaml
# docker-compose.test.yml
version: '3.9'

services:
  test:
    build: .
    command: pytest -v
    environment:
      - DATABASE_URL=postgresql://test:test@testdb:5432/testdb
    depends_on:
      testdb:
        condition: service_healthy

testdb:
    image: postgres:15-alpine
    environment:
      POSTGRES_USER: test
      POSTGRES_PASSWORD: test
      POSTGRES_DB: testdb
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U test"]
      interval: 5s
      retries: 5
```

---

## 배포 서버 초기 설정

서버에서 최초 1회:

```bash
# docker-compose.yml 복사 또는 git clone
git clone https://github.com/your/repo.git /app
cd /app

# .env.prod 생성
cp .env.example .env.prod
# ... 값 채우기

# 최초 실행
docker compose --env-file .env.prod up -d
```

이후부터는 Actions가 자동으로 `docker compose pull && up`.

---

## 이미지 태그 전략

```
latest     — main 브랜치 최신
sha-abc123 — 특정 커밋 (롤백용)
v1.2.3     — 릴리즈 태그
```

롤백:
```bash
# 이전 버전으로 롤백
docker compose down
IMAGE_TAG=sha-abc123 docker compose up -d
```

---

## 정리

1. **테스트** — Compose로 격리된 환경에서 실행
2. **빌드** — `docker/build-push-action`으로 GHCR에 푸시
3. **캐시** — `cache-from: type=gha`로 빌드 시간 단축
4. **배포** — SSH로 서버 접속 → `docker compose pull && up`
5. **롤백** — SHA 태그로 언제든 이전 버전으로 복귀 가능

"GitHub Actions로 Docker 자동 빌드·배포"

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