🚀 Cloud Migration & 3-Tier Web Application

A complete 3-Tier web application architecture containerized with Docker Compose, plus a one-command automated deployment script (deploy.sh) for migrating to a production Linux cloud server (GCP, AWS, Azure, DigitalOcean).

Portfolio goal: Demonstrate cloud migration skills, Docker networking, multi-tier architecture design, and CI/CD-ready deployment automation.

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🌟 Architecture Overview

Internet
    │
    ▼
┌─────────────────────────────────────────┐
│  Tier 1: Nginx (Reverse Proxy)          │
│  Port 80 — serves static files +        │
│  proxies /api/* → Flask                 │
└──────────────────┬──────────────────────┘
                   │
                   ▼
┌─────────────────────────────────────────┐
│  Tier 2: Flask Application Server       │
│  Port 5000 (internal) — REST API        │
│  Connects to PostgreSQL via SQLAlchemy  │
└──────────────────┬──────────────────────┘
                   │
                   ▼
┌─────────────────────────────────────────┐
│  Tier 3: PostgreSQL Database            │
│  Port 5432 (internal only)              │
│  Persistent volume — survives restarts  │
└─────────────────────────────────────────┘

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🛠️ Requirements

Local development:

• Docker Desktop

Cloud deployment:

• A Linux VPS (Ubuntu 20.04+) with SSH access
• SSH key pair configured

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🚀 Quick Start (Local)

# 1. Copy environment template
cp .env.example .env

# 2. Start all 3 tiers
docker compose up -d --build

# 3. Access the application
# Frontend: http://localhost
# API Health: http://localhost/api/health
# API Items:  http://localhost/api/items

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☁️ One-Command Cloud Deployment

chmod +x deploy.sh
./deploy.sh <YOUR_SERVER_IP> <SSH_USER>

# Example:
./deploy.sh 34.126.120.50 ubuntu

What deploy.sh does automatically:

1. rsync — copies project files to the remote server
2. Installs Docker if not already present
3. Runs docker compose up -d --build on the server
4. Performs HTTP health check on /api/health
5. Reports success or failure with the public URL

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📡 API Endpoints

Method	Endpoint	Description
GET	/	Nginx-served frontend landing page
GET	/api/health	Health check — returns {"status": "ok"}
GET	/api/items	List all items from PostgreSQL
POST	/api/items	Create a new item {"name": "..."}

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📁 Project Structure

16_cloud_migration_3tier_app/
├── .github/workflows/ci.yml    # Build validation CI
├── app/
│   ├── app.py                  # Flask API server
│   ├── requirements.txt
│   └── Dockerfile
├── nginx/
│   ├── nginx.conf              # Reverse proxy config
│   └── html/
│       └── index.html          # Landing page
├── db/
│   └── init.sql                # PostgreSQL schema + seed
├── docker-compose.yml          # 3-tier orchestration
├── deploy.sh                   # One-command cloud deploy
├── .env.example                # Environment variables template
└── README_VI.md                # Vietnamese documentation

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⚙️ Environment Variables

cp .env.example .env

Variable	Default	Description
POSTGRES_DB	appdb	Database name
POSTGRES_USER	appuser	DB username
POSTGRES_PASSWORD	(set in .env)	DB password — never hardcode
FLASK_ENV	production	Flask environment

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🔒 Security Notes

• Database credentials are loaded via .env — never committed to Git
• Database port (5432) is not exposed externally — internal Docker network only
• Nginx acts as the only public-facing entry point