Amazon Web Services EC2 – Part 4: Transient Storage
Elastic Compute Cloud (EC2)
The storage that comes with an AMI is called Transient Storage. That means that when the instance is stopped, the storage goes away. Any data or files saved when the instance was running is lost. This is by design.
To persist your data between sessions, you have two options. During most of the beta period, the Simple Storage Service (S3) was the only internal method of persisting data. S3 cannot be mounted as file system so it served as a backup service only.
Shortly before the beta period ended, Amazon added the Elastic Block Store (EBS). EBS is a mountable disk device. For database oriented applications, EBS is pretty much mandatory.
Some applications may not need EBS. For example, a web-based catalog lookup may only use the storage that is contained with the AMI. Whenever the catalog changes, the AMI can be updated directly. This would allow you to mount as many catalogs (new AMI instances) as you needed when you needed to scale.
The important take away here is that your application will need to plan (and pay) for persistent storage if your application has the need for non-transient storage.
Both S3 storage and EBS will be explored in detail in the near future.