I have a Windows-based Amazon EC2 instance with an EBS drive as the root device. Is it possible to launch a copy of this instance without creating an AMI – for instance, from a snapshot of the C: drive? We'd like to test something on a clone of the server without having to shut it down (which seems to happen if we try to create an AMI).
Launching AWS Windows instance from snapshots
amazon ec2amazon-amiamazon-ebswindows-server-2008
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An AMI, as you note, is a machine image. It's a total snapshot of a system stored as an image that can be launched as an instance. We'll get back to AMIs in a second.
Lets look at EBS. Your other two items are sub-items of this. EBS is a virtual block device. You can think of it as a hard drive, although it's really a bunch of software magic to link into another kind of storage device but make it look like a hard drive to an instance.
EBS is just the name for the whole service. Inside of EBS you have what are called volumes. These are the "unit" amazon is selling you. You create a volume and they allocate you X number of gigabytes and you use it like a hard drive that you can plug into any of your running computers (instances). Volumes can either be created blank or from a snapshot copy of previous volume, which brings us to the next topic.
Snapshots are ... well ... snapshots of volumes: an exact capture of what a volume looked like at a particular moment in time, including all its data. You could have a volume, attach it to your instance, fill it up with stuff, then snapshot it, but keep using it. The volume contents would keep changing as you used it as a file system but the snapshot would be frozen in time. You could create a new volume using this snapshot as a base. The new volume would look exactly like your first disk did when you took the snapshot. You could start using the new volume in place of the old one to roll-back your data, or maybe attach the same data set to a second machine. You can keep taking snapshots of volumes at any point in time. It's like a freeze-frame instance backup that can then easy be made into a new live disk (volume) whenever you need it.
So volumes can be based on new blank space or on a snapshot. Got that? Volumes can be attached and detached from any instances, but only connected to one instance at a time, just like the physical disk that they are a virtual abstraction of.
Now back to AMIs. These are tricky because there are two types. One creates an ephemeral instances where the root files system looks like a drive to the computer but actually sits in memory somewhere and vaporizes the minute it stops being used. The other kind is called an EBS backed instance. This means that when your instances loads up, it loads its root file system onto a new EBS volume, basically layering the EC2 virtual machine technology on top of their EBS technology. A regular EBS volume is something that sits next to EC2 and can be attached, but an EBS backed instance also IS a volume itself.
A regular AMI is just a big chunk of data that gets loaded up as a machine. An EBS backed AMI will get loaded up onto an EBS volume, so you can shut it down and it will start back up from where you left off just like a real disk would.
Now put it all together. If an instance is EBS backed, you can also snapshot it. Basically this does exactly what a regular snapshot would ... a freeze frame of the root disk of your computer at a moment in time. In practice, it does two things different. One is it shuts down your instance so that you get a copy of the disk as it would look to an OFF computer, not an ON one. This makes it easier to boot up :) So when you snapshot an instance, it shuts it down, takes the disk picture, then starts up again. Secondly, it saves that images as an AMI instead of as a regular disk snapshot. Basically it's a bootable snapshot of a volume.
Can i create a S3-backed / instance-store AMI out of an EBS based instance?
Yes, you can create an Instance-store AMI out of an EBS based instance.
- Install ec2-ami-tools in the instance
- Upload your x509 certificates to the instance
- Use ec2-bundle-vol and ec2-upload-bundle commands NOTE: You need your account ID, Access Key and Secret Key to run these commands
- Register the image specifying the bucket/manifest name where you have uploaded the image files.
Step by step documentation can be found at http://docs.amazonwebservices.com/AWSEC2/2008-02-01/GettingStartedGuide/?ref=get-started Refer the Creating an Image section of this guide.
Can i create S3-backed / instance-store instance from EBS based AMI?
No you can't
Best Answer
By default, when creating an AMI image of an EBS-boot instance, the instance will be shutdown. The benefit of shutting down is that the filesystem is ensured to be in a consistent state (no partial file writes).
Using the Amazon AWS Management Console, you're forced to stop the instance when creating the AMI image. However, when using the API or command-line tools, you can choose to avoid the shutdown.
If you don't want to create an image, you can duplicate your instance from a regular snapshot. To do this:
The new instance should resemble the original instance as long as the file system is good.
Essentially it's like duplicating a hard drive of a working PC, buying a new PC and replacing the hard drive in the new PC with your duplicate hard drive.