[ec2-beta] ec2 concepts and understanding

[Jim Cheetham]

On Mon, Mar 30, 2009 at 9:28 AM, Darryl <smartssa at gmail.com> wrote:
> I'm just wondering about how persistent these instances are supposed to be
> on the EC2 cloud.

An AMI is a read-only "image" of a machine. In itself it doesn't do
anything, and doesn't run. It's just the equivalent of files on a
disk.

An 'instance' is a running virtual machine. An instance starts with an
AMI, and the equivalent of being "switched on" and booted from disk.

An instance lives in EC2 memory only. There is no permanent storage
associated with it, unless you configure EBS or S3 specifically for
it. The filesystems that you see in an instance are virtual; they will
still be there if you reboot your instance, but once you stop it,
Amazon releases the whole associated memory, and the instance is lost.

There are two approaches to the public AMIs :-
 * Start a public AMI, configure it for your own use (including
installing software) every time you use it
 * Start a public AMI, configure it, then create a new AMI that lives
in your own S3 storage location. Next time, start your own AMI, not
the public one.

-jim