Vendors hawking them include the likes of Hewlett-Packard Co. and IBM, Linux purveyors Red Hat Inc. and Novell Inc., and independent support providers such as SpikeSource Inc., OpenLogic Inc., SourceLabs Inc. and many others.
Yet a growing number of critics say that stacks has already become a hyped-up buzzword that fails to serve many users.
"Stacks are rigid and deterministic," said Winston Damarillo, CEO of Simula Labs Inc., a Marina Del Rey, Calif., open-source software provider. They are "prefab solutions, which most customers don't really want in the first place."
Take Davis Tharayil, CIO at Home Insurance Co., for example. Tharayil is looking for a cheaper alternative to the Oracle databases on Solaris servers the in-liquidation insurer runs now. Tharayil is testing a custom server appliance built by rPath Inc. with the open-source Ingres database running on a stripped-down version of Linux. Even though Tharayil was looking for a plug-and-play product, at no point did he consider a precertified open-source application stack.
"A full stack just wasn't necessary," Tharayil said. Besides, he added, "I've been in the business for 35 years. Every time something new comes along, they say it's a silver bullet. And I still haven't found one."
Application stacks have a long history in the proprietary software arena. Vendors such as Microsoft Corp. and Oracle Corp. have long marketed their integrated product line to customers as a way to boost interoperability and cut costs, though critics say that also leads to customers facing vendor lock-in.
In open source, most software providers remain small, offering at most a handful of applications rather than entire lineups. That put the responsibility on corporate users, or their highly paid consultants, to ensure that the software worked together -- something that could easily wipe out the savings from using free software.
The first true open-source stack emerged during the dot-com boom in the form of Web servers. Dubbed LAMP, it included the Linux operating system with the Apache HTTP Web server and MySQL database on top, supported by code written in languages such as Perl, Python or PHP. LAMP's popularity woke up vendors to the potential of packaging and testing open-source applications in a tidy way, cutting deployment time and risks for companies, especially smaller ones.
That has led to the emergence of dozens of LAMP imitators, as well as open-source software stacks running on Windows, dubbed WAMP. Critics call it a flood of poorly tested, not-very-well-integrated stacks.
"When you try to certify everything from soup to nuts, it ends up not meaning much at all," said Erik Troan, chief technology officer at rPath.
Others said that despite the apparent bounty of open-source stacks, they don't begin to meet the particular needs of many companies. "Many open source stack providers can only afford to support the most popular open source components. There are so many open source projects that no single vendor can assemble the expertise to meet every customer need," declared The 451 Group in an August report critical of open-source stack providers.
One firm trying to do something a little different is Simula Labs. Led by Damarillo, who founded and sold open-source application server vendor Gluecode Software Inc. to IBM in 2005, Simula provides enterprise support for open-source software. But rather than being just another MySQL, JBoss or Apache support provider, Simula is supporting technically sound but more niche-oriented products. In the process, it is getting in front of senior IT managers right away.
"With Gluecode, we used to have it sneak into departments," Damarillo said. "With Simula Labs, we're starting with the CIO."
Simula Labs emerged from stealth mode last week with support for four open-source applications. It has already signed 50 contracts worth an average of $80,000 per year with 20 mostly large organizations, according to Damarillo. Those deals include the State of Colorado and the National Institutes of Health.
Others, such as Troan, argue that customers who buy into open-source stacks can become as locked in as if they had bought a closed-source stack. They become afraid to deploy new applications "for fear you could break 50 other applications," he said. He claimed that rPath's software appliances grant customers the same easy deployment promised by stacks -- without those downsides. Besides Ingres, SugarCRM Inc. and open-source VoIP provider Digium Inc. are offering their software via rPath appliances.
Dennis Callaghan, an analyst at The 451 Group, likes what rPath is doing, though he noted that the company has "a pretty small niche and customer base at this point."
The marketing of open-source stacks won't disappear overnight, said James Governor, an analyst at Denver-based RedMonk, because their tidiness still appeals to some customers. But their rigidity will make them less relevant as more companies expect the true standards-based component modularity that service-oriented architectures promise, he said.