Welcome To The Cloud. Please Place Your AMI (Whatzat?) HereWelcome To The Cloud. Please Place Your AMI (Whatzat?) Here

Does cloud computing sound like fun, something your department or business unit could do while waiting for IT to come up with that new system you requested two years ago? Why not make use of somebody else's computing infrastructure, especially if they're smart enough to figure out how to give you access to it?I'll bet those 10-cent per hour charges can be hidden in the budget somewhere.

Some such thinking, in part, is driving current interest in cloud computing. While warranted, I'd like to point out one thing about the cloud that hadn't occurred to me before.

On the Amazon Elastic Compute Cloud FAQ, it raises the question, "How do I load and store my system on EC2," and answers by explaining that the customer will need to generate an Amazon Machine Image. It says:

"An Amazon Machine Image (AMI) is simply a packaged-up environment that includes all the necessary bits to set up and boot your instance. Your AMIs are your unit of deployment. You might have just one AMI or you might compose your system out of several building block AMIs (e.g., webservers, appservers, and databases)." The experienced VMware or XenSource customer immediately recognizes that the Elastic Compute Cloud is running virtual machines, which makes eminent sense, and you will be shipping the software you want to run in EC2 in some kind of virtual machine format. In fact, the reference to AMI is simply a disguised name for yet another VM format, like VMware's VMDK or Microsoft Hyper-V's and XenServer's VHD.

I thought the Amazon Cloud, when it relied on virtual machines, was running the open source Xen hypervisor on Linux servers, which also made sense to me. But what's AMI about? Virtual Iron, Sun, Oracle and Citrix XenServer are all based on Xen and none of them use an AMI format.

And I can hastily add, I don't know the answer, other than to point out Amazon has taken the open source hypervisor, tweaked it for its own purposes and come up with its own VM format. It provides its customers the tools to convert their software bits into the format, ship it up to Amazon S3 storage, and from there, activate the machine image in a Xen-like virtual machine.

This isn't at all unusual. For the record, Sun uses its own format with Xen-based xVM, not to mention VDI or Virtual Disk Image, with its desktop VirtualBox.

So let the buyer, if not beware, be at least well informed. You may be gaining an experimental test bed in the cloud for your next project, but you're also gaining another virtual machine format, one that you haven't seen before and one hopefully you won't have to understand in too much detail. What happens in the cloud, stays in the cloud, we hear -- or was that just a weary VMworld attendee as he stumbled home from Las Vegas?

Meanwhile, you can get back to struggling with those proliferating "free" Hyper-V VMs and those paid-for VMware VMs and all the ways they don't work with each other.