You will be converting the current state of an EC2 system to an AMI, which is an image that you can use to start new EC2 instances. This can be needed when certain providers or amazon machine images (AMI) are originally created with instance-store bootable hard drives. I had to use a Rightscale AMI which unfortunately did not use EBS, but the instance-store storage method. EBS volumes are persistent and bootable, while instance-stores reset themselves to their original state when restarted.
I did this after the install of the application, Zenoss. If you want an EBS version of the base OS, you could do this conversion process before installing any application like Zenoss. If you do it post app-install, with nothing else loaded or touched, you will have an image of a clean duplicable zenoss setup that you could use to create new app-ready instances over and over. Because of this, you might want to make sure that the state of the running server instance is clean, stable, and base.
Below are the rough steps that were used:
ec2-register --snapshot snap-9eb4ecf6 --architecture i386 --name "Zenoss Enterprise 3.0 beta 2 on centOS" --description "Blah" --root-device-name /dev/sda1 --kernel aki-9b00e5f2
If you want details on any steps, I compiled this by following instructions from both of the following websites: