Welcome to Crystal Ball Sunday #8! Today's discussion focuses on Virtual Appliances which are small virtual machines designed for a very specific purpose. There are Virtual Appliance Email servers, VPN servers, Firewalls, Routers, Dial-in servers, DNS servers, CMS application servers, and the list goes on and on.

I had this Crystal Ball vision while writing the virtual networking and storage chapter of my upcoming book, Practical Virtualization Solutions (Pearson/Prentice Hall). In this chapter, I was explaining how to create a VPN server virtual machine using Windows 2003 Server when I had the brainstorm that there were probably some Virtual Appliances built for this sole purpose. I was right! I found several on the VMware Appliance Marketplace website and began downloading and testing them to include in the book.

What suprised me was the small footprint and low memory requirements of these appliances. You can download a VPN server Virtual Appliance that uses less than 150MB of disk space and 64MB of RAM. Truly revolutionary considering that a comparable installation of Windows 2003 Server is over 2GB!

Linux is a perfect choice for Virtual Appliances because of its infinite customizability options, ability to be placed on, and run from, a Live CD, its licensing and distribution rights, and of course it's free.

Several companies and independent vendors create freely available Virtual Appliances that you can download and use for free. Try out a few of these locations for starters: VMware, ThoughtPolice, and JumpBox. Most of the available Virtual Appliances are VMware virtual machines but some also exist for other virtualization technologies as well. For those of you who need or require commercial support, it is generally available through the supplying vendor.

Most of the virtualization technologies today are built on Linux--VMware and Xen are the big names in the business--especially in the HyperVisor end of virtualization. Virtual Appliances are the next big deal in the world of virtualization--so if you're into virtualization in any capacity, you need to learn about Virtual Appliances and how you can leverage them for your own use.