The open source Linux operating system offers a lot of compelling  advantages in virtualized environments. The platform’s inherent flexibility and modular design makes it possible to reduce overhead by omitting unneeded components. Instead of virtualizing an entire general purpose operating system, you can use a minimalistic profile that bundles only the bare necessities and the dependencies that you need to deploy your application. These slim platform images are often referred to as “Just Enough Operating System” (JeOS) software appliances.

An entire class of new tools is emerging to help developers and system administrators generate JeOS images. Such tools can generate bootable system images in several formats with the components selected by the user. Some of the more sophisticated tools even have automatic dependency resolution features that can guess what packages will be needed by analyzing a target application. Many of these tools are designed to build images that are based on specific Linux distributions.

One of the most powerful tools in this field is rPath’s Builder platform, which can create virtual images based on several several distributions, including CentOS and Ubuntu. It offers support for numerous output formats including those compatible with VMware, Microsoft Virtual PC, Virtual Iron, Parallels Workstation, and Xen. It also recently gained support for the  Amazon Machine Image format, which is used by Amazon’s Elastic Compute Cloud service. The rBuilder platform leverages the advanced Conary package management system to perform automatic dependency resolution.

The Ubuntu Linux distribution also provides its own unique solution for JeOS construction. The vmbuilder tool, which is designed to be used at the command line, is a quick and easy way to generate custom Ubuntu images. It is generally used with KVM and it’s particularly useful for software developers who want to create self-contained Ubuntu server testing environments.

There are a lot of emerging JeOS tools that are still under development. Novell’s SUSE Studio, which is still in closed alpha testing, provides an extremely rich graphical user interface for building SUSE appliance images with custom packages, special configurations, and custom branding. SUSE Studio has several default profiles that can be used to quickly create images with complete GNOME and KDE environments or a lightweight text-only environment.

With some of the latest tools, the process of building virtual appliances is just as easy as selecting a set of packages from a web-based package management interface. As JeOS tools become more sophisticated, the challenges associated with generating custom platform images will swiftly decline.