https://itmanual.net/cloud-computing-%ea%b8%b0%ec%b4%88-2-%ed%81%b4%eb%9d%bc%ec%9a%b0%eb%93%9c-%ec%84%9c%eb%b9%84%ec%8a%a4-%ec%a2%85%eb%a5%98-%ed%8d%bc%eb%b8%94%eb%a6%ad-vs-%ed%94%84%eb%9d%bc%ec%9d%b4%eb%b9%97/