需要的資源與服務，都在雲端上。通常都是用多少算多少，相對的傳統機房不是建太多就是不夠用。
各種雲端比較
| Component | EnterpriseIT | IaaS | PaaS | SaaS |
|---|---|---|---|---|
| Application | ✓ | ✓ | ✓ | |
| Security | ✓ | ✓ | ||
| Database | ✓ | ✓ | ||
| OS | ✓ | ✓ | ||
| Virtualization | ✓ | |||
| Servers | ✓ | |||
| Storage | ✓ | |||
| Network | ✓ | |||
| Data Centers | ✓ |
Note: IaaS 的特點應該是可以操作系統層級，PaaS 是可以撰寫指定的語言，SaaS 則是只能使用軟體
Feature
Business Benefits of Cloud
- Almost zero upfront infrastructure investment，幾乎不用前期投資在基礎建設上
- Just-in-time infrastructure，隨開即用
- More efficient resource utilization，更高的資源利用率
- Usage-based cosing，用多少算多少
- Reduced time to market，節省資源溝通時間
Technical Benefits of Cloud
- Automation - “Scriptable infrastructure”
- Auto-scaling
- Proactive Scaling
- More Efficient Development lifecycle
- Improved Testability
- Disaster Recovery and Business Continuity
- “Overflow” the traffic to the cloud