休眠模式主要是透過保留記憶體內的內容 (會寫到 EBS 裡)，讓機器開起來比較快，不過這邊有要求 root EBS volume 需要加密：
When an instance is instructed to hibernate, it writes the in-memory state to a file in the root EBS volume and then (in effect) shuts itself down. The AMI used to launch the instance must be encrypted, as must the root EBS volume of the instance. The encryption ensures proper protection for sensitive data when it is copied from memory to the EBS volume.
費用的部分是 EBS volume 與 Elastic IP：
While the instance is in hibernation, you pay only for the EBS volumes and Elastic IP Addresses attached to it; there are no other hourly charges (just like any other stopped instance).