Virtual software appliances are applications -- mostly server ones, at this point -- that come to users prepackaged with a thin operating system layer. Essentially virtual machines (VM) created by independent software vendors or systems integrators, rather than IT administrators, virtual software appliances help eliminate potential conflicts with the host hardware's operating system or other applications, reducing crashes and improving security.
Many vendors are enthusiastic about virtual software appliances. They include virtualisation players such as rPath and VMware; Linux vendors such as Red Hat, Canonical and Novell; and application vendors such as Oracle.
For instance, Novell is working on a SUSE Studio tool kit that will allow vendors to easily build virtual appliances of their applications on top of a JEOS (just enough operating system) version of SUSE Linux Enterprise 11.
Market research firm IDC also likes the long-term prospects for virtual software appliances. Though it only expects the market to total US$156.3 million (NZ$279 million) this year, IDC predicts US$1.2 billion worth of virtual software appliances to ship in 2012. Linux-based appliances will be neck and neck with those that are Windows-based, with each having almost half of the market, and Unix-based appliances running a distant third.
The mainstreaming of server virtualisation as well as preconfigured hardware appliances (think LAMP Web servers or Oracle's Database Machine) is enabling corporate IT to accept virtual software appliances.
According to the results of an IDC survey released in February, 20% of 302 IT managers at US companies said they were already running some software appliances in production, up threefold from 7% the year before. Mid-size companies are deploying them the most, with network management and business applications such as ERP the most popular.
Despite the promising data and the vendor support, virtual software appliances are no sure bet to catch on, according to Gordon Haff, an analyst at Illuminata.
"The idea makes a lot of intellectual sense, but IT folks haven't really bought into it," he says.
For one, virtual software appliances try to smooth things in the datacentre by taking the operating system out of the equation. That's a radical notion to many, Haff says.
"Frankly, IT is used to the idea that operating systems are sort of important. They are used to having to qualify and certify software for specific OS versions," he says. "The idea that the OS is part of the app? That is a big leap."
Others on the corporate IT side, such as Peter Schmidt, director of business intelligence at Centro, amedia planning firm, say they prefer the control of building virtual machines themselves rather than taking them straight from vendors.
"We do a lot of stuff in-house anyway," says Schmidt.
Haff agrees, pointing out that Linux operating systems such as Red Hat and Novell's SUSE Linux Enterprise "are already fairly modular.
"You can already choose to not install all of the roles or packages in Linux, and achieve a 'soft JEOS' effect," he says. "Large IT shops do exactly that."
Also, while virtualisation and Linux vendors love virtual software appliances, Windows-centric ones such as Citrix and Microsoft do not. Microsoft, in particular, "has a great self-interest in ensuring that the operating system remains extremely relevant," Haff says. Such companies are instead pushing application virtualisation as an alternative.
Independent software vendors that are simultaneously being pulled toward putting their applications into the cloud or onto virtual software appliances are often putting off the latter.
For example, Pentaho recently released a cloud version of its open-source business intelligence software. But it hasn't seen enough customer demand to stride down the virtual software appliance route.
"There's a lot of talk, but I haven't seen much demand for people to procure a virtual software appliance straight from us," says Lance Walter, Pentaho's vice president of marketing.