Simple Virtual Appliances with Linux and Xen

Next, let's package up the appliance and then go through the motions of deploying it as mysql.example.com. To package up the appliance, simply tar up the disk image and configuration:

xenhost$ cd /xen/appliance-base
xenhost$ tar -cvzf appliance-base.img appliance-base.cfg
xenhost$ mkdir /xen/mysql.example.com
xenhost$ cd /xen/mysql.example.com
xenhost$ tar -xvzf /xen/appliance-base.tar.gz
xenhost$ mv appliance-base.cfg /etc/xen/auto/mysql.example.com.cfg
xenhost$ vim /etc/xen/auto/mysql.example.com.cfg

Edit the Xen configuration file /etc/xen/auto/mysql.example.com.cfg as shown in Listing 4. Set the name, the path to the disk image, and give this guest a unique MAC address. Placing the configuration under /etc/xen/auto means the appliance will be started automatically when the Xen host boots.

name   = "mysql.example.com"
memory = "256"
disk   = ['tap:aio:/xen/mysql.example.com/appliance-base.img,xvda,w',]
vif    = ['bridge=xenbr0,mac=00:16:3e:00:00:02',]
vcpus  = 1

bootloader = "/usr/bin/pygrub"
on_reboot  = 'restart'
on_crash   = 'restart'

Start the new appliance using the following command:

xenhost$ xm create /etc/xen/auto/mysql.example.com.cfg
xenhost$ vm console mysql.example.com

Examine the console output as the guest boots; the last bit of output will have the DHCP-assigned IP, thanks to your rc.local additions. Point a Web browser at the URL shown; by default, Webmin listens on TCP port 10000. Once logged in as root, you will be able to manage your MySQL appliance. Webmin will allow you to set a static IP, maintain YUM updates, create additional users, configure firewall rules, create and maintain MySQL databases and tables, and configure automated system and MySQL backups.

Using these simple steps and readily available components, you can create a thin virtual appliance to do almost anything. Because its a virtual machine, you can move it between physical computers and deploy it multiple times with ease.

As I stated in the introduction, all of these steps could have been done with VMware virtualization products. VMware is certainly the most widely deployed technology and has its own tools for creating virtual appliances, including an on-line “Appliance Marketplace” for sharing prebuilt appliances. No matter whether you use VMware or Xen, virtual appliances are a simple way to deploy preconfigured services with minimal hassle. If you are a software author, it allows you to hand your customers a “known working configuration” every time.