What data is stored in Ephemeral Storage of Amazon EC2 instance?

Question

I am trying to stop an Amazon EC2 instance and get the warning message

Warning: Please note that any data on the ephemeral storage of your instance will be lost when it is stopped.

My Question

What data is stored in ephemeral storage of an Amazon EC2 instance?

Answer 1

Ephemeral storage is a temporary storage for storing data such as cache, buffers, swap volume, session data, etc. For example, when you create an AMI of your instance's current state, it will contain everything in what we call as ephemeral storage. This ephemeral storage is replicated to EBS volume automatically by AWS to prevent data loss. The instance launched using this AMI will contain everything in normal instance store volume, the volatile temporary storage that only exists during the running lifetime of the instance.

Answer 2

Anything that is not saved on an EBS volume that is mounted to the instance will be lost.

For example, if you mount your EBS volume at /mystuff, then anything not in /mystuff will be lost. If you don't rise an ebs volume and save stuff on it, then I believe everything will be lost.

You can build an AMI from your current machine state, which will contain everything in your ephemeral storage. Then, when you start a new instance based on that AMI it will contain everything as it is now.