NEIL ASPINALL

There has been a recent explosion of network appliance-based products, ranging from Web servers and caching Web proxies to file servers and firewalls. But what exactly is a network appliance and why are many industry analysts proclaiming that Linux will be successful in this market?

An appliance is a network server much like a traditional NT or UNIX server. But, rather than operating as a general purpose server, network appliances, also known as "thin servers", are usually dedicated to one task.

Dataquest defines a thin server as:

"a specialized, network-based hardware device used by businesses, and designed to perform a single or specialized set of server functions. It is characterized by running a minimal operating architecture, and client access is independent of any operating system or proprietary protocol. The device is a 'closed box,' delivering extreme ease of installation and minimal maintenance, and can be managed remotely from a Web browser."

-- The Gartner Group (http//www.dataquest.com)

As noted in the preceding quote, one of the main benefits of network appliances over traditional servers is ease of installation and use. Most can be configured and maintained using simple "fill-out-forms" in an ordinary Web browser like Netscape. Others use a simple client/server application designed specifically for the configuration and maintenance of that appliance. All aspects of the appliance are configured from that one interface, whereas in a traditional server, networking might be configured with one tool, and event logging with a completely different tool. In addition to easing the set-up process, the integrated Web based configuration model also simplifies the ongoing administration and maintenance of the network appliance.

The fact that network appliances are largely self-contained devices contributes much to their ease of configuration. While traditional servers are able to support a vast array of peripherals and third party software, network appliances are limited to a small subset of expansion options. This allows the appliances to focus on ease-of-use for the tasks they do perform. For example, rather than supporting a multitude of third party network adapters like a traditional server, networking is built into an appliance, and the appliance's software comes pre-configured to use it.

Many other factors contribute to the easy installation and maintenance of network appliances. For example, those that are equipped with a hard disk come with all the necessary software pre-installed and mostly pre-configured. The remaining configuration tasks are often child's play.

One such "hard disk equipped" server is the "Cobalt Qube" by Cobalt Networks (formerly Cobalt Microserver). To get a Qube up and running, you only need to attach it to the network and assign it an IP address. The Qube has simplified this by allowing users to set its IP address and host name using some buttons and an LCD on the back of the box.

For those appliances which have no hard disk, set-up is even simpler. Enter a few configuration parameters, and let it run. With so little chance of configuring it improperly, there is a greater chance that it will work properly the first time, and keep working properly indefinitely. A less advanced appliance might have a set-up scheme more like that of a router or other traditional networked device, but in any case, an appliance can usually be up and running on the network in less than 20 minutes.

The last key ease-of-use feature network appliances specialize in is remote management. They are built from the ground up with remote management capabilities in mind. The ability to configure or maintain the server using a consistent interface from any location with an Internet connection and a Web browser greatly eases the tasks of administration.

Linux for Appliances

So what do network appliances have to do with Linux? Well, because of the robust and compact Linux kernel, a number of network appliance designers have chosen Linux as their operating system.

The kernel, which is the heart of the operating system, provides the interface between the computer hardware and the applications. While the Linux kernel is compact, it is also tremendously flexible, and supports a large number of platforms and peripherals. The ability to customize the Linux kernel to match the specific appliance hardware and peripherals makes it the ideal OS for manufacturers to base their products on.

Also, the Open Source licenses under which the Linux kernel and a majority of other Linux software are released make it easy for appliance manufactures to build customized software on a solid foundation. This, coupled with the fact that the source code is available to all, makes the software easy to customize -- the only stipulation being that the customized software also be made available under the terms of the GNU General Public License (GPL).

The number of developers contributing to both the Linux kernel and other Open Source Software projects is large and growing steadily. This trend in software development has important ramifications for appliance manufacturers. As more people contribute new software and ideas to Open Source projects, their reliability and feature sets will increase. These benefits will then be quickly realized by the network appliances.

In many cases, features added to Open Source projects show up in products that use the software almost immediately. Often, all that is required for the manufacturer to incorporate a software update is some customization to the user interface followed by a small amount of testing and debugging. This means companies which build products on Open Source Software can add new features and bug fixes with little effort. This allows these companies to focus on simplifying the configuration and administration of their devices.

Using Linux as the core for a network appliance allows the manufacturers and their OEM partners to easily port new software to the appliance. This is due to the industry standard POSIX Application Programming Interfaces (APIs) used in the Linux kernel. In addition, most of the more common network applications, such as the Apache Web server, already run on Linux.

Many companies believe the business model for Open Source-based products to be somewhat unclear. Most still believe that in order to be successful, their software must be kept as a very closely guarded trade secret. This myth is being partially dispelled by companies such as Netscape as they embrace the Open Source model. The network appliance manufacturers seem to be creating yet another Open Source business model. By embedding Linux and Open Source software in their own hardware, they are creating highly salable products and clear revenue streams.