Corporations should look at virtual appliances as a way to create a highly customised platform to run their applications, VMware co-founder and chief scientist Mendel Rosenblum said in a keynote at Linuxworld in San Francisco.

Today's operating systems cater to a wide variety of applications and user cases, which has lead to an explosion of the size of both Linux and Windows. This in turn makes it hard to maintain the code, increasing the overall number of bugs as well as the chance of security vulnerabilities remaining undetected.

Developers also have to optimise their applications for multiple operating systems, which requires time and money.

Instead, Rosenblum recommended, developers should consider creating a custom operating system.

"Rather than making your application run on a bunch of different operating systems, you choose one operating system. You bundle it together and you ship this thing around as a virtual appliance," Rosenblum said.

Linux is the ideal candidate to run these virtual appliances because the operating system is free and open source.

An application-specific operating system doesn't just cut back on the potential number of bugs and security flaws. Developers can also add features that increase the software's performance.

Several companies are currently selling virtual appliances. Database vendor Ingress for instance is shipping a virtual appliance based on a specialised Linux distribution that is maintained by rPath.

In June Middleware maker BEA started shipping its WebLogic Server Virtual Edition, a virtual version of its Java application server that allows users to quickly add compute power to Java applications that are part of a Service Oriented Architecture.

The jury on virtual appliances however is still out, because each customised Linux version is essentially a fork.

Red Hat for instance in May started shipping what it referred to as a database appliance running the Sybase database. The partnership, however, was a straightforward software bundling agreement and didn't involve a customised version of Red Hat Linux optimised for the database.

"We won't compromise the reason people go to open source and Linux in the first place, which is to have a platform that is well tested and developed by the community," Scott Crenshaw, Red Hat's vice president for Enterprise Linux said at the time.

"There are lines that have to be drawn to optimise the security and quality. You can expect a great degree of customisation to be available, but not the creation of a Linux fork."

Rosenblum expects that there will be a degree of standardization around software appliances that prevents an explosion of Linux distributions for which developers have to develop patches and updates and that requires hardware certification.

In addition to specialised companies such as rPath, existing Linux vendors could also create customisable versions of their distributions that can be tweaked for certain applications, VMware suggested.

• A video of Rosenblum discussing virtual appliances is available on vnunet TV